Things don’t change without something triggering it, so there are a few things to be looking at. If it was a single item that had changed I’d think a staff member was part of that. Since it’s not a single item, and you’re suggesting content has also reverted it makes me assume you’ve got some product management app, an ERP, third party POS connector - or something - in place. Do you have something that syncs data from another system?
That’s what I would look into first, along with any app you have installed that can modify products.