I've tried various versions of 15.x.x Cura for Linux 64 bit. When I look at the views/layers I can see if skit and brim are being generated in the Gcode. If under "Support" any Platform adhesion type is selected (brim or raft) NO Skirt will be generated REGARDLESS of what settings you've made in the Expert Config menu for Skirt Line count or Start distance. Once you turn off the Platform adhesion type (set to None), THEN SKIRT is generated. Slicer lets you generate BOTH skirt and brim, (and it has a bug in that it lets the two run into each other if you have the diameter and distance settings wrong). It seems that Cura may be trying to perform a test to see if the Skirt will run into the brim or raft and not print the Skirt if it does, but that test ALWAYS fails and no Skirt is printed, EVEN if it would be safe to do so. I haven't gone back in time to try any Cura 14.x.x versions, but from postings on this forum I suspect this bug is in those versions also.