Spot the difference 
Im soooo happy with this small modification. It went from zero objects printed okish to 100%
I give up. What’s the mod?
Added fan?
Is that a Felix?
Yep its a felix 2.0, Im printing parts for my #morgan-reprap. the small mod is the mk8 extruder drive gear pulley.
I saw the mk8 right after I posted. That was my next guess.
Same issue with the original gear on the Felix 2… The issue is the dog pulling the bearing against it starts twisting, causes the filament to push unevenly into the hot end, jams, strips, back to no prints.
Most problematic extruder ever I swear. That was only the beginning of my fun, next the piece attached to the stepper warped. Misalignment again. The base of that assembly warped, replaced that with aluminum. Eventually completely replaced that rubbish on mine, part makergear part custom, just as reliable as my up plus 2 now!
Good luck. Keep away from ABS and Nylon otherwise you will end up with the issues I had. Lucky I had a second printer to print parts with to bring it back to life!