I did set buffer back to 20. There are two things what changed a) now PP always break-up with an error-message, which 8. b) the time till error 8 occurs is longer. Before that, error 8 came constantly in the break between end of first song and the beginning of the next song. After I set buffer down to 20 error 8 occurs spotty but not within a song.
It does not seem to have anything to do with OS-activities, because I did plug in and unlocked screen, could not see any OS action but same error 8.