The DX7 and the AR7000 are ussually very solid and reliable.
If this combination was faithful and worked for you before, your problem lies in the new setup:
BEC power may not be clean or enough under load...
or your plane/RX has a RF Blind spot.
I don't like to use a BEC on anything larger that a 2 lbs foamy, or a 450 heli, that's me.
Don't like DS821 on anything more that a training or sport plane, too many output gears failures on record.
Now I'm guessing if it was my fault because I got disoriented from being so far away. I don't thing this is the case because I was taking it easy, slow level flying.
What can I say?
How many times have you lost orientation flying easy like you said in the last month, year? If zero, then dont guess yourself unless the scheme on the Extra was hard to see to begin with.
If everything checks ok, try the RX on a small foamy or cheap plane to check functionality and range. If RX the exterior looks damaged, send it in.OR
Mount the motor, esc and radio a board or rig mimicking the Extra.
Do a ground test with the AR7000, the log recorder, and all servos pluged in. Put a your grount tester on a 360 holder/fixture, walk away and have someone slowly spin the rig to test all orientations. Check the log.
, Borrow someone else DX7 if you can, repeat the ground test or foamy test again to make sure is not your TX, just in case.