The plane was flying along fine in straight and level flight and suddenly would not respond to the "radio" sticks. What would you like to blame ryanpilot, the family dog? Sorry but it seem obvious that something in the radio system is acting up whether it is the rx, batt, switch harness or whatever is what has to be determined. An intermittent condition is entirely possible, I see them daily on the full scale aircraft radios I work on. A micro-fracture or a little solder ball rolling around inside the rx case can drive you crazy. You could always send any suspect parts to the mfg with a good description of the incidents so they will know what they are looking for. The more information you provide a tech, the better your service will be. Nothing is worse than a complaint like "don't work right". The tech can run hot/cold tests as well as vibration and check the boards under a microscope for damage. Or you can just throw money at the problem and buy a new rx and battery pack.

Good luck either way.