RE: Almost crashed 1/4 Scale CUB Floatplane yesterday...
I agree that the problem could be in the switch. I had one that balked twice about powering up the receiver and it quickly hit the trash can and it was not very old.
On another vein, check the fail safe position that it is not closing the throttle so far as to shut down the motor. Going to idle is what is wanted as it can sometimes be the quickest warning that you are losing control.
What you describe however is very consistent with a known quirk of the G-20 if the spark plug boot was not seated fully. Was the radio ranged checked with engine running? The G-20 is very reliable but if the spark plug boot is not fully bottomed on the plug, a great deal of interference is generated from arching within the boot and it is easy to miss that the boot is not fully seated as it takes a lot of effort to get it fully in place. A good idea is to clamp the boot onto the plug with a very small hose clamp to insure that it stays in place.
I'm thinking you may have had rfi generated at the spark plug boot and the fail safe shut the throttle fully down killing the motor.