Ok, I flew with AQ boards also proabably for more then 50h - on quads, Y6 and octos. The problems started when moving with the octo from 3S (no problems for many h) to 4S (sometimes a flight without crash, sometimes after a few seconds). It is a F8 with X2212 motors and ultraESC. I also tried 4S on a quad with cheap simonk esc, no problems (>1h) - so I started to think about the esc causing trouble. I observed the issue with- and without gimbal, bluetooth, sd-card...
Is this the first time that you combined 4s, AQ and kissESC (same developer as for the ultraESC)? I tried to check all the lines with a scope but I was not able to find something directly related to the freezing. Would be interesting if it is related to the use of some esc at a certain voltage ...
It is still the issue I was discussing with teramax in Friedrichshafen... I also wrote about it in an other thread:
viewtopic.php?f=31&t=3086&hilit=phynix - back then I hoped that it would be solved with an other board with DIMU - but unfortunately this is not the case. I spend hours, maybe days in tracking down the error - without much success. It demotivated me a little bit - and I felt a little bit lost with it. So I started looking around for an other FC with the same capabilities as it is hard to trust something with these findings. But if there is now an other case that sounds similar, I am willing to spend more time for solving this with a little bit of support! If you like, we can also talk directly ...