A Microsoft file hosting and synchronization service.
For me it just started happening today, 23 Feb 2025, both on PC & Mac. I need to move some files between shared folders, tried with the web interface and the "Move here" button is grayed out... the phone app started to re-sync all 3000+ photos that were already synced .. Funny how when i was in the phone app it popped a message asking for a review.. and while i was writing my issues with the service and the iOS / Android apps.. it crashed..
The service gets worse and worse by the years. I had since quite some time the idea to switch to a private cloud solution, and these issues are just a catalyst for this..