I have the HEXA B...love it and have about 20 hours of flight time on it.
Recently I have been having an Issue: First start of the day and all six motors perform flawlessly. But..the next start seems to always have the #2 motor go into a jerky mode. I replaced the engine and that made no difference. I always manage to get all 6 spinning, but not until after some pillow talk.
I have made a video where the issue is quite clear. At 1 + 15 minutes, even the #1 engine momentarily fails to spin up, but managed to spin up after a power increase.
I would like to pay one million bitecoins <sic erat scriptum> to the person that helps me figure this out.
Found 2 bad ESC's causing the problems. R&R'ed the parts and now have ops normal. (BTW, "all-at-once" ESC's Calib. did not work. Had to do them individually. HEXA B)