I have not experienced that problem, but I can hypothesize. It could be your USB drive isn't a good fit in the slot. With cooling and warming, the drive and the slot will both shrink and swell. If they lose contact, the system will think you pulled it out and revert to the radio.
Maybe just try a different USB drive. It might be a better fit. Good luck!
Maybe just try a different USB drive. It might be a better fit. Good luck!