I have this problem too. Using the wired headset (any of various) when the phone has the lockscreen engaged, a double-click results in a pause action instead of a skip. A triple click is the same. But sometimes it skips to the next song, and pauses at the same time. I have to click again to get the song to play. The beeps are confused, sometimes only one, sometimes both together, sometimes none at all, and no action. Sometimes I pause, and it takes a, couple of seconds for the command to be processed. This did NOT happen before v905-uni. I enter settings, and set skip to long click, then back to double-click again, and it works OK for a couple of songs, then back to the problem again.
Double-click works with the rest of my audio apps: Smart Audiobook player, Black player, Spotify, just not PA.
Moto G9 plus, Android 10. But there haven't been any recent updates to Android, not even a security update since March, and the problem is more recent.