Hi guys, after a while i found your conversation, and i think I've found a solution.
I'm printing on an UM2+, upgraded from UM2. I#m using NinjaFlex and Semiflex. I've had a lot of trouble printing it. Sometimes the tube was not clean enough (old strings of ninjaflex) or simply there was not enough pressure by the extruder. Then it cam out ok, with a bit under-extrusion. My settings are 134 celsius nozzle, 70deg bed. Then i went to Cura and changed the nozzle to 0.6 coming from 0.4. The result blow we away after i changed everything to an multiplier of the nozzle size. Retraction off, fans off, everything at 30mm/s. So this means i'm printing layers at 0.3, shell at 1.2 cause nozzle is 0.6. I don't know maybe i never read the right page in the manual, but this changed drastically the printed result. Also semi flex (TPU95) is much easier than Ninjaflex (TPU85) which in my opinion is simply to elastic for the overall construction.