First of all My escs and radio were calibrated.
At startup randomly one motor does not start after about 3-4 three minutes successfull run.
If motor starts there is no problem it continues to start and spin.
On my video look at startup, 2.07 and 3.00.
My Quad config is:
Pixhaw with Arducopter 3.2.1
H4 Aliena 680 frame with Aerialmob landing gear
TM-MN4010 370Kv Motors
RCTimer 15x5.5 Propeller
16A Gens Battery
3DR GPS Kit
The only time I had this happen to me turned out to be a faulty ESC... it started out with the motor randomly not starting up on arming... then progressed to not starting at all. It was a fairly quick progression, however, over the course of may a couple days before it failed all together. The only other thing I can think of is did you try calibrating your ESCs individually? I have read that calibrating all at once can sometimes not work, though I have never had this issue. Hope this helps in some way.
I think i solved the problem.
I change THR_MIN value to 150 and RC_SPEED value to 100.
I found this solution while searching in forums.
Maybe THR_MIN change could be enough.
I tested this at ground level.
I will fly as soon as possible and We will see the results.