I have the same problem since June 2022. In March 2022, I updated to Android 10 from Android 9 on my OnePlus 5T and a couple months later, this issue drives me crazy. I have reached out to Poweramp and Maksim did reply to me, but after my last explanation of what is going on in the log I sent versus what I did on the phone, I haven't received any response.
I am slightly convinced that this has something to do with the Android OS, but one would think it would happen to everyone from Android 10 up.
Here's something to test to see if it works: when you're experiencing the problem, open up Poweramp, go to Settings, then Misc, and then press Restore Defaults button (take note of your settings first if you have anything customized on this page... I do not). Doing this makes it function correctly again until I connect Android Auto.
Hopefully we can get some light shed on this topic sometime soon. No other audio player has this issue for me.
Best,
Mike