BUG: Audio tracks not playing or levels are changed after returning to a project
14.3.1. Opening a project that has not been worked on for a few days or weeks, various audio tracks simply don't play, or play at greatly reduced volume. Either 1) Soloing and unsoloing the track, or 2) in any way modifying the audio level on that track will fix the problem.
Matt Stegner commented
Can you send an affected project file (.prproj) to firstname.lastname@example.org, attention Matt so I can investigate?