I was dry testing my pixhawk quad build with the motors spinning (props off) and moving it around by hand to check all is good and it suddenly disarmed and stopped. Yeah just like that.
Did it few times actually when I proceed to test some more.
The only thing that i've changed recently is BRD_SAFETYENABLE parameter, which I set to 0 to disable the need to press the safety button every time. (I hate safety) and have left the physical button plugged in because I like the way it lights.
Could this be a reason? Have you ever a disarm happen just like that while "flying"?
p.s. funny thing is this parameter was NOT visible through APM GS software but was in Tower android app.