Hi there, I've just print and installed 2 of the Neotko FatIRobert on my um2+ i'm having similar issue as @derbroti with the 2.85mm.
I have lots of play ( that I was able to resolve with some washer) and reprinting a the arm.... but no matter what I'm getting some serious under-extrusion issue.
I've been playing now for 2 days, taking apart,checking an tuning my Thinkergnome firmware but i cannot seems to resolve the issue.
Any one that can help on the matter?