A Microsoft file hosting and synchronization service.
I can confirm that this general approach works. Starting again and using a new location for your OneDrive files seems to do the trick. I don't think you need to use the App Store app though. I unlinked my computer in OneDrive preferences then deleted the app and then re-installed from the app downloaded via the Microsoft site. The re-synced to a new locations and voila. So relieved! Well done to Kayne for working it out. I found another smart soul on Reddit before I read this, however if it wasn't for that you would have been my saviour Kayne :)