Filament grinding

[jjl71194 0]

Hi I've been having a problem with my UM2 recently where the bowden extruder will stop pushing filament through the tube and instead just grind down the filament. I've tried using the atomic method to clean the nozzle and it came out clean. I've opened up the bowden extruder and cleaned out any plastic scraps there. The spring in the bowden extruder is at the lowest tension. The printer will print fine for one print after cleaning out the bowden extruder and using the atomic method, then it will go back to grinding instead of extruding filament for the next print. I print using both ABS and PLA. Can anyone help me fix this? Thanks.