Pasting the relevant portions of the log:
2016-09-02 17:25:14,671 - INFO - UM/Backend/Backend.pyc (startEngine [55]): Started engine process: /Applications/Cura.app/Contents/MacOS/CuraEngine
2016-09-02 17:25:14,672 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] Calling engine with: ['/Applications/Cura.app/Contents/MacOS/CuraEngine', 'connect', '127.0.0.1:49674', '-j', '/Applications/Cura.app/Contents/Resources/cura/resources/definitions/fdmprinter.def.json', '']
2016-09-02 17:25:14,672 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend]
2016-09-02 17:25:14,673 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] Cura_SteamEngine version DEV
2016-09-02 17:25:14,673 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] Copyright © 2014 David Braam
2016-09-02 17:25:14,673 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend]
2016-09-02 17:25:14,673 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] This program is free software: you can redistribute it and/or modify
2016-09-02 17:25:14,673 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] it under the terms of the GNU Affero General Public License as published by
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] the Free Software Foundation, either version 3 of the License, or
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] (at your option) any later version.
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend]
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] This program is distributed in the hope that it will be useful,
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] but WITHOUT ANY WARRANTY; without even the implied warranty of
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
2016-09-02 17:25:14,674 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] GNU Affero General Public License for more details.
2016-09-02 17:25:14,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend]
2016-09-02 17:25:14,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] You should have received a copy of the GNU Affero General Public License
2016-09-02 17:25:14,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] along with this program. If not, see .
2016-09-02 17:25:14,682 - DEBUG - UM/Backend/Backend.pyc (_logSocketState [165]): Socket state changed to Connected
2016-09-02 17:25:14,683 - DEBUG - UM/Backend/Backend.pyc (_onSocketStateChanged [155]): Backend connected on port 49674
2016-09-02 17:25:15,201 - DEBUG - .../cura/plugins/CuraEngineBackend/CuraEngineBackend.py (_onStartSliceCompleted [222]): Sending slice message took 0.04148578643798828 seconds
2016-09-02 17:25:15,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] [ERROR] Unregistered setting mesh_position_x
2016-09-02 17:25:15,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] [ERROR] Unregistered setting mesh_position_y
2016-09-02 17:25:15,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] [ERROR] Unregistered setting mesh_position_z
2016-09-02 17:25:15,676 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] [ERROR] Unregistered setting center_object
2016-09-02 17:25:15,677 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] [WARNING] -s support_interface_height="1" -s shell="0" -s retraction_speed="25" -s support_infill_rate="15" -s speed_print="60" -s jerk_layer_0="20" -s wall_thickness="0.8" -s jerk_support="20" -s experimental="0" -s switch_extruder_retraction_speeds="20" -s support_extruder_nr="0" -s cool_fan_full_at_height="0.3" -s cooling="0" -s wall_line_width="0.4" -s material="0" -s platform_adhesion="0" -s dual="0" -s travel="0" -s travel_compensate_overlapping_walls_enabled="True" -s support="0" -s jerk_wall="20" -s speed_support="60" -s resolution="0" -s acceleration_support="3000" -s infill_overlap="10" -s jerk_print="20" -s meshfix="0" -s speed_wall="30.0" -s blackmagic="0" -s speed="0" -s machine_settings="0" -s wireframe_flow="100" -s wireframe_roof_outer_delay="0.2" -s wireframe_roof_drag_along="0.8" -s wireframe_roof_fall_down="2" -s wireframe_strategy="compensate" -s wireframe_drag_along="0.6" -s wireframe_top_jump="0.6" -s wireframe_flat_delay="0.1" -s wireframe_bottom_delay="0" -s wireframe_top_delay="0" -s wireframe_flow_flat="100" -s wireframe_flow_connection="100" -s wireframe_printspeed_flat="5" -s acceleration_wall="3000" -s wireframe_printspeed_down="5" -s wireframe_printspeed_bottom="5" -s wireframe_roof_inset="3" -s wireframe_height="3" -s wireframe_printspeed_up="5" -s magic_fuzzy_skin_thickness="0.3" -s support_conical_min_width="5.0" -s support_conical_enabled="False" -s skin_alternate_rotation="False" -s skin_outline_count="0" -s support_interface_density="100" -s coasting_enable="False" -s draft_shield_height="10" -s draft_shield_height_limitation="full" -s draft_shield_dist="10" -s draft_shield_enabled="False" -s magic_spiralize="False" -s raft_fan_speed="0" -s magic_mesh_surface_mode="normal" -s raft_speed="30.0" -s infill_mesh="False" -s print_sequence="all_at_once" -s meshfix_keep_open_polygons="False" -s ooze_shield_dist="2" -s ooze_shield_angle="60" -s ooze_shield_enabled="False" -s multiple_mesh_overlap="0.15" -s prime_tower_wipe_enabled="False" -s prime_tower_flow="100" -s prime_tower_position_y="200" -s wireframe_nozzle_clearance="1" -s prime_tower_position_x="200" -s prime_tower_size="0" -s support_extruder_nr_layer_0="0" -s adhesion_extruder_nr="0" -s raft_base_fan_speed="0" -s bottom_thickness="0.8" -s machine_max_jerk_e="5.0" -s skin_overlap_mm="0.02" -s raft_interface_jerk="20" -s wireframe_up_half_speed="0.3" -s raft_surface_acceleration="3000" -s support_interface_extruder_nr="0" -s support_line_distance="2.6666666666666665" -s raft_interface_speed="22.5" -s material_print_temperature="200" -s raft_base_line_spacing="1.6" -s raft_surface_line_spacing="0.4" -s raft_surface_line_width="0.4" -s cool_fan_speed="100.0" -s coasting_min_volume="0.8" -s prime_tower_enable="False" -s raft_surface_thickness="0.1" -s raft_interface_line_width="0.8" -s machine_disallowed_areas="[]" -s infill_sparse_density="20" -s jerk_support_interface="20" -s support_bottom_distance="0.1" -s raft_surface_layers="2" -s raft_airgap="0.3" -s raft_margin="15" -s brim_line_count="20" -s extruder_prime_pos_z="0" -s acceleration_prime_tower="3000" -s skirt_gap="3" -s extruder_prime_pos_y="0" -s conical_overhang_angle="50" -s retraction_retract_speed="25" -s extruder_prime_pos_x="0" -s support_tower_diameter="3.0" -s retraction_enable="True" -s support_interface_line_distance="0.4" -s raft_acceleration="3000" -s support_bottom_height="1" -s support_interface_enable="False" -s support_join_distance="2.0" -s material_standby_temperature="175" -s support_bottom_stair_step_height="0.3" -s support_xy_distance_overhang="0.2" -s support_xy_distance="0.7" -s wall_line_width_x="0.4" -s raft_base_thickness="0.36" -s support_top_distance="0.1" -s machine_nozzle_tip_outer_diameter="1" -s support_pattern="zigzag" -s support_offset="0.2" -s jerk_travel_layer_0="30.0" -s support_type="everywhere" -s cool_lift_head="False" -s cool_fan_speed_min="100.0" -s retraction_prime_speed="25" -s cool_min_speed="10" -s cool_fan_enabled="True" -s travel_avoid_distance="0.625" -s jerk_print_layer_0="20" -s jerk_support_infill="20" -s raft_interface_fan_speed="0" -s jerk_topbottom="20" -s jerk_wall_x="20" -s acceleration_enabled="False" -s jerk_wall_0="20" -s magic_fuzzy_skin_enabled="False" -s jerk_enabled="False" -s infill_mesh_order="0" -s raft_base_speed="22.5" -s speed_travel="120" -s layer_0_z_overlap="0.15" -s machine_max_acceleration_y="9000" -s acceleration_skirt_brim="3000" -s acceleration_travel_layer_0="5000.0" -s travel_avoid_other_parts="True" -s acceleration_print_layer_0="3000" -s jerk_infill="20" -s acceleration_support_interface="3000" -s raft_surface_jerk="20" -s acceleration_support_infill="3000" -s acceleration_wall_0="3000" -s machine_head_with_fans_polygon="[[-20, 10], [10, 10], [10, -10], [-20, -10]]" -s retraction_combing="all" -s acceleration_infill="3000" -s wireframe_fall_down="0.5" -s speed_equalize_flow_max="150" -s speed_equalize_flow_enabled="False" -s top_bottom_pattern="lines" -s skirt_brim_line_width="0.4" -s cool_fan_full_layer="0" -s cool_min_layer_time_fan_speed_max="10" -s speed_slowdown_layers="2" -s skirt_brim_speed="30" -s support_enable="False" -s conical_overhang_enabled="False" -s speed_travel_layer_0="60.0" -s raft_jerk="20" -s speed_print_layer_0="30" -s raft_interface_thickness="0.15000000000000002" -s infill="0" -s magic_fuzzy_skin_point_dist="0.8" -s coasting_speed="90" -s support_infill_extruder_nr="0" -s speed_prime_tower="60" -s speed_support_infill="60" -s raft_base_jerk="20" -s speed_wall_x="60.0" -s machine_max_jerk_xy="20.0" -s extruder_prime_pos_abs="False" -s gradual_infill_step_height="5.0" -s speed_wall_0="30.0" -s switch_extruder_retraction_speed="20" -s retraction_hop="1" -s retraction_hop_only_when_collides="False" -s retraction_hop_enabled="False" -s acceleration_wall_x="3000" -s coasting_volume="0.064" -s machine_min_cool_heat_time_window="50.0" -s retraction_amount="6.5" -s skirt_line_count="1" -s retraction_count_max="90" -s prime_tower_line_width="0.4" -s machine_max_feedrate_e="25" -s material_flow="100" -s machine_height="300" -s raft_base_acceleration="3000" -s switch_extruder_retraction_amount="16" -s material_bed_temperature="60.0" -s jerk_skirt_brim="20" -s machine_heat_zone_length="16" -s infill_wipe_dist="0.1" -s travel_compensate_overlapping_walls_x_enabled="True" -s infill_overlap_mm="0.04" -s machine_max_acceleration_e="10000" -s infill_pattern="cubic" -s alternate_extra_perimeter="False" -s material_print_temp_wait="True" -s retraction_hop_after_extruder_switch="True" -s speed_layer_0="30" -s raft_surface_speed="30.0" -s skirt_brim_minimal_length="250" -s layer_height="0.1" -s infill_line_distance="6.0" -s machine_name="FDM Printer Base Description" -s z_seam_type="shortest" -s retraction_extrusion_window="6.5" -s xy_offset="0" -s infill_sparse_thickness="0.1" -s speed_topbottom="30.0" -s retraction_extra_prime_amount="0" -s support_area_smoothing="0.6" -s travel_compensate_overlapping_walls_0_enabled="True" -s raft_base_line_width="0.8" -s wireframe_straight_before_down="20" -s support_line_width="0.4" -s acceleration_layer_0="3000" -s retraction_min_travel="0.8" -s machine_start_gcode="G28 ;Home
2016-09-02 17:25:15,677 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G1 Z15.0 F6000 ;Move the platform down 15mm
2016-09-02 17:25:15,677 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] ;Prime the extruder
2016-09-02 17:25:15,678 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G92 E0
2016-09-02 17:25:15,678 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G1 F200 E3
2016-09-02 17:25:15,678 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G92 E0" -s brim_width="8.0" -s wall_0_inset="0" -s raft_surface_fan_speed="0" -s raft_interface_acceleration="3000" -s support_minimal_diameter="3.0" -s machine_max_acceleration_x="9000" -s speed_support_interface="40.0" -s material_print_temp_prepend="True" -s machine_max_feedrate_z="5" -s magic_fuzzy_skin_point_density="1.25" -s wall_line_count="2" -s meshfix_union_all_remove_holes="False" -s material_diameter="2.85" -s top_layers="8" -s support_interface_line_width="0.4" -s wireframe_printspeed="5" -s machine_acceleration="4000" -s support_roof_height="1" -s infill_line_width="0.4" -s machine_max_feedrate_x="500" -s machine_width="200" -s gradual_infill_steps="0" -s machine_show_variants="False" -s skin_line_width="0.4" -s support_z_distance="0.1" -s layer_height_0="0.3" -s wall_line_width_0="0.4" -s acceleration_print="3000" -s machine_heated_bed="True" -s line_width="0.4" -s machine_minimum_feedrate="0.0" -s material_extrusion_cool_down_speed="0.5" -s machine_nozzle_head_distance="3" -s machine_max_acceleration_z="100" -s raft_interface_line_spacing="1.0" -s cool_min_layer_time="5" -s machine_max_jerk_z="0.4" -s machine_use_extruder_offset_to_offset_coords="True" -s machine_nozzle_size="0.4" -s jerk_travel="30" -s jerk_prime_tower="20" -s acceleration_topbottom="3000" -s machine_max_feedrate_y="500" -s meshfix_extensive_stitching="False" -s bottom_layers="8" -s gantry_height="99999999999" -s material_bed_temp_wait="True" -s material_bed_temp_prepend="True" -s machine_depth="200" -s machine_nozzle_cool_down_speed="2.0" -s max_feedrate_z_override="0" -s machine_nozzle_heat_up_speed="2.0" -s support_conical_angle="30" -s brim_outside_only="True" -s meshfix_union_all="True" -s infill_before_walls="True" -s material_flow_dependent_temperature="False" -s adhesion_type="brim" -s support_tower_roof_angle="65" -s cool_fan_speed_max="100.0" -s acceleration_travel="5000" -s machine_nozzle_expansion_angle="45" -s support_use_towers="True" -s support_connect_zigzags="True" -s machine_extruder_count="1" -s machine_head_polygon="[[-1, 1], [-1, -1], [1, -1], [1, 1]]" -s machine_center_is_zero="True" -s wireframe_enabled="False" -s support_interface_pattern="concentric" -s material_flow_temp_graph="[[3.5,200],[7.0,240]]" -s support_xy_overrides_z="z_overrides_xy" -s top_bottom_thickness="0.8" -s support_angle="50" -s machine_gcode_flavor="RepRap" -s switch_extruder_prime_speed="20" -s top_thickness="0.8" -s machine_end_gcode="M104 S0
2016-09-02 17:25:15,678 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] M140 S0
2016-09-02 17:25:15,678 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] ;Retract the filament
2016-09-02 17:25:15,679 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G92 E1
2016-09-02 17:25:15,679 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G1 E-1 F300
2016-09-02 17:25:15,679 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] G28 X0 Y0
2016-09-02 17:25:15,679 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] M84" -s skin_overlap="5" -s speed_infill="60" -s skin_no_small_gaps_heuristic="True" -g -e0 -s extruder_prime_pos_x="0" -s machine_extruder_end_pos_y="0" -s machine_nozzle_offset_y="0" -s machine_extruder_end_pos_x="0" -s machine_extruder_end_pos_abs="false" -s machine_nozzle_offset_x="0" -s machine_extruder_start_pos_y="0" -s extruder_prime_pos_z="0" -s machine_extruder_start_pos_x="0" -s machine_extruder_start_pos_abs="false" -s extruder_prime_pos_y="0" -s machine_name="Extruder" -s extruder_nr="0" -e0 -l "0"
2016-09-02 17:25:17,773 - DEBUG - UM/Backend/Backend.pyc (_backendLog [88]): [backend] Assertion failed: (false && "We should have returned already before here!"), function insert, file /Users/Ultimaker/build/2.3/build/CuraEngine-prefix/src/CuraEngine/src/utils/SparseLineGrid.h, line 112.
2016-09-02 17:25:17,773 - DEBUG - .../cura/plugins/CuraEngineBackend/CuraEngineBackend.py (_onBackendQuit [412]): Backend quit with return code -6. Resetting process and socket.
I just tried this from source and I couldn't reproduce it. Could mean that someone already fixed it. Could you also give me the logs? That way I can verify if your issue is actually solved.