In the latest update, 12.1.1, audio playback has become unreliable
Often, audio tracks will not play as video plays.
The issue can be solved by muting and then unmuting or soloing and then unsoloing channels. The problem is only present on playback, not on export.
Tom Werber commented
OK! That's much worse. This is a serious bug which I have experienced multiple times over two separate projects on different systems now.
Peter C commented
I've had this happen on an export too. Part, not all, of the timeline was mute. I was using 5 or 6 audio tracks, none of them were muted or soloed.