I'm getting really sick of this happening to me. Every so often we go camping in remote areas of Australia. Every time over the last few years before we have gone Poweramp has worked perfectly while in the city. Then, after being out of contact for a few days, Poweramp fails its license check and stops working. We haven't done a software update. We haven't even rebooted. It just stops working. Then we have no music player until we get some mobile coverage again - sometimes 1-2 weeks later.
I don't believe the FAQ at all. It isn't just a problem with the latest version - it happened last year, and the year before, and the year before. This time it happened on 3 of my devices. It is usually 3-4 days after last internet contact.