Series of old files and now lost audio

I've read the" Audio is Missing" Article. Ran through the checklist and it still doesn't make since why my audio just disappeared. I had just listened to a Preview of some slides and there was audio, I saved my PPTX, but kept the Powerpoint open  -- a few hours later --- poof, they were gone!  Now I had this happen a year ago, but it was my fault renaming some files. This time I did nothing of the kind.

I have noticed (see attachment) a collection of old-ppta files building u over the past couple of weeks. Actually, never seen that before to this extent. Does this have anything to do with the lost audio?

I restored my audio files manually and resync'd -- don't want this to happend again, of course.

Can you help?

Thanks,

Jann