A Microsoft file hosting and synchronization service.
My (temporary) fix that worked for me (I tried many suggestions in this thread) was to uninstall OneDrive, install it again, login, re-add Sharepoint data to it, let it sync. It would stay fixed for a day or 2 weeks. Repeat when it happened again. However this particular problem was eventually resolved by Microsoft. It took them a month or 2 and this issue one day completely disappeared from our office. Hopefully it's not coming back again but considering I saw another post like this 3 years ago, who knows. Just FYI