No failsafe to me means something else happened unrelated to a signal issue, otherwise you would have had a failsafe event..
It can be an internal cause. I've seen everything from plugs, extensions, ignition noise, servos, etc. cause what looks to be a radio issue. None of those is going to result in a failsafe since that is triggered by loss of RF signal.
If you like I can reach out to Brian O'Meara who also has a large P-47 to see if he can shed any light.