I've used Poweramp (full version) for many years very happily - it's easily the best music player available for Android. However, I had a very frustrating experience recently that I feel shouldn't ever happen.
I was on a long (5 hour) flight and I was listening to music through Poweramp for the first couple of hours of the flight. I stopped the music briefly while I ate some food on the flight and when I restarted Poweramp I was told that it couldn't validate my licence as there was no internet access and thus Poweramp refused to start. Since I was on a plane and hence didn't have any means of obtaining internet access, that meant that I couldn't use Poweramp for the remainder of the journey. I don't understand why, after two hours of happily playing, it would suddenly decide that the licence is no longer valid without an internet connection. I have now been forced to look for other music players (preferably without licensing) so that I can travel without losing access to my music part-way through the flight.
I realise it's hard to control licensing and you don't want a situation where people can use it without paying if they put their phone on flight mode while playing music, but there must be a better way of dealing with it than locking out the player while in use. Can't there at least be a grace period of (say) a day if the licence has previously been validated and the problem is lack of internet access?
I'm using Poweramp 2.0.10-build-588-play (Full Version) on a Oneplus 5 running stock Android 8.0.0.