I returned today from a trip to London. An hour or so into the flight Poweramp again stopped working with the usual message about being unable to verify the license without an internet connection. So for the remaining nine hours of the flight to Los Angeles I couldn't use this app. I don't think that I have ever completed a transatlantic or transpacific flight and not have PA stop working once disconnected from the internet. Other users must be using PA on airplanes, so why does it always happen to this installation?
For the record, the hardware is a Zenfone 2 running Android 5.0. The Poweramp Version/Changelog shows "2.0.10-build-860588-x86-play (Full Version)". Now that I'm connected to the internet, the Poweramp About page also confirms with a check mark "Purchase Verified Store: Play". I have never reinstalled PA (although at this point maybe I should), installed a new ROM, or reset the system.
Hoping that the problem might go away is obviously not a viable solution, so what is the next step?