Sound keeps disappearing

Hi! I keep having an issue where sound just disappears from Premiere Pro. It was there, in the timeline, I can hear it in the monitor - and then it's just gone. I'm not doing complicated proper editing - just removing some audio tracks from a single file and outputting it.

It seemed random at first but then I realized it seems to happen when I click outside Premiere Pro to go do something else for moment.  If the other thing has a potential sound component (even if I'm not using it), like Teams chat box or a web browser or opening the file I just exported in QT to check it - when I go back to Premiere, sound there is gone. If I try to export a file at that point, it will not have sound on it, and I cannot hear or see sound in the timeline. If I click away while the waveform is generating, it will only have like half of it done when I go back.

Weird thing is, this is a suddenly new thing. I used to be able to click on other windows and apps and go back to Premiere without any problems - still using this same version (2021) and same OS (Big Sur). I have no idea why this has started and was hoping someone knew WTF is going on. I can't think of anything that has changed.

Other similar posts on here I found said to check the preferences for audio hardware and set it to No Input but mine is already that. Others said to clear the cache which does work usually - but it is annoying to have to do that repeatedly, especially since I have to quit and reopen to clear the whole cache.  Is there a way to fix this or is this just an annoying glitch I have to deal with?