Hexa motor fail


I got my Hexa ready this week and got it fly pretty well (APM 2.6 3.2.1). But yesterday one motor (#6) started to fail after 30-60sec fly without any reason (i didn’t change any settings). When it happened first time, copter was pretty high and it recovered after tilt so fail is temporary but it happen in every flight. Same fail happen in stabilize, alt and loiter mode. I’m pretty new with APM and i don’t have any idea how i should start to trouble shot this. Is the problem DJI 920kv 2212 motor, ESC Neewer® M-30A 30A 5V/3A 2-4SLIPO 5-12SNIMH Simonk ESC (with BEC), or APM.

Any help would be nice
Thank you

Obviously reason was bullet connectors. I soldered all cable connections and after that it stopped to fail.