"I had the same issue with ArduPlane 2.7 on 2 different APM 2.5's.  Are you by chance using the uBlox GPS?  I was getting the artificial horizon start to jump around with the uBlox attached.  I swapped the uBlox out for a MediaTek and the issue went…"

"I get the same behavior with my APM2 board.  When I connect to the board via USB, it resets, the ABC lights come on and there is some TX activity.  Then A(red) turns off and stays off.  When I look at the MissionPlanner console, I see the following:…"