"I went back to 2.9.1 firmware, which is where I was originally having the resets, and I am NOT able to reproduce the problem.
Here's a summery of my testing, all on the test rig:
Firmware 2.9.1:
1) In stabilize mode, 11 minute flights, 2 flights…"

"Removing the external LEDs from the APM had no effect; it still reset during AltHold. 
I also attached an oscilloscope to the +5V and ground rails of the input connections.  It never deviated from the attached screenshot.  The software doesn't…"

"I've been able replicate the problem while having a video camera watching it in close range.  You can see the LEDs go out with the motors continuing their last command for a few seconds before they shut down.

In the video, it shuts down at 0:47.…"

"Add my issues to the list that are similar to this discussion. I've heard the ground station say 'disarmed' after the drop began and didn't think anything of it at the time.

http://diydrones.com/forum/topics/hexicopter-rolls-90-degrees-and-d..."

"Had a new strangeness today.   Seems that loiter won't hold when I changed the yaw (possibly coincidence).  The telemetry shows the loiter 0-1 meters from the loiter beginning point but you can see that it's moving quickly north.
It was doing well…"

"I've just begun trying to tune my HexCopter using the How to Tune 2.8.1 thread.  First I'm attempting to tune is the Rate parameters, setting the RATE_K parameters to the Channel 6 knob.  I reduced the Rate P to 0.12 from 0.15 to begin with as it…"

"I'm looking at trying to reduce the vibrations caused by my motors and props.  I've balanced the APC 10x4.7 props using a Dubro balancer and balanced the motors with a seismic app on my android phone and separately, everything is pretty clean.  When…"

"Did a run with about 8 WPs and the copter finished successfully.  When it completed the waypoints, we attempted to use the RTL from the Actions tab in Mission Planner.  At that point, all motors shut off.  About 5 meters above ground they started…"