Please... I have plenty of apps that use Google's paid app system, and none that are so unreliable as Poweramp. This is so obviously an integration problem, and continuing to just blame it on Google is ridiculous.
Poweramp chose to use a Google library, among the many libraries that any application needs. If a chosen library is failing, it is up to the app's developer to make it right. You don't just blame the library and wash your hands of it. The library was your choice, and so it is your responsibility to fix. You can code a workaround, replace the library with something else, or provide amnesty for those experiencing the problem. It is unacceptable to blow off your customers, while continuing to sell the app.