A Microsoft file hosting and synchronization service.
Exact same thing is happening here.
I'm an author and didn't realize a massive 240,000 word document I've been editing has not been being saved properly. When I turn on sync, it saves a new copy, and I have trouble finding that copy because I used to just be able to go to my Documents, Open, Edit, and it would auto-save to the cloud from there while I edit. It's like the new documents disappear into a void when I enable auto-save. Now I have to search for OneDrive in my computer first, to find what is hopefully the right document, which is annoying as heck. I can't check over 240,000 words every time to make sure everything is correct, so this is insane.
I didn't realize how much this had been happening. When I finally found the location where my documents were being saved when I Enabled Auto-Save again, I found a trove of repeat documents I had kept trying to Auto-Save but couldn't find where they would normally upload. I'm beyond livid.
I think the difference here for me is that I really had trouble finding where these "new" repeat documents were being saved, and I had given in to manually saving new documents to my PC, which has created a lot of confusion... I don't know which is the real document anymore, since I likely made mistakes along the way. I'm glad I have Atticus for authors. I paid once for their application and cloud service, and so I think I will just migrate everything to there and leave Microsoft365.
edit: Literally after I posted this, my "disappeared" documents (which are all slightly different repeats of each other, because of the Auto-Save being off by default) are appearing in my Documents folder now. I must've done something after getting frustrated for the past couple of months, but I don't know what. I don't know if the problem will be fixed from now on... time will tell, so I'll give it a go a bit longer.