Hi Keith
I had/have done all that you itemised above. I am an electonic techo by trade, so I think I have god fault finding logic.

It is possible though, if the rx is faulty, for it to just stop working.
The battery voltage is good
I run 5 cells, no voltage regulator. I have always done that, with all my planes, rx's.

regarding the outside loops, the plane had bit of speed on, so it was easy to achieve. And let's face it, was it 2 or 3 times. The main point is, it was holding the elevator at the last know input, AND I heard the engine cut back to idle.