Hmmm .... I messed up. I overlooked one of my sync locations. I thought Barcoding and Communications site were SharePoint locations made from Teams. However, it turns out that Communications Site and Company Site were the same location. I'm not sure how I managed to get that SharePoint folder synced under 2 different locally named folders.
I removed both the Communications site and the Company Site from syncing ... and the re-added Company Site by itself. It appears to be working properly now. I probably could have simply removed the Communications site and it would have cleared up the problem.
I understand there's likely no need to sync a SharePoint folder locally under two different names ... but It really doesn't fully explain why the files would upload and then disappear. It also doesn't explain why only graphic files (png, jpg, etc.) disappeared and Excel spreadsheets would stick.