File sync can be changing the names if that folder (with the photo storage) is one of the files being synced.
I recommend:
1. Un-sync the photo folder,
2. Split the main folder into smaller ones with whatever naming you like eg, cars, school, kids etc
You already know about tagging (and more power too you) but I'd still suggest Lightroom to help you organize… it's non invasive and designed for large collections.
Windows has a limit on the amount of file space any folder can store and it is a major risk having so many photos all together in the same place.
Jpg images aren't the best stock because every time you edit them a little bit of quality is lost