iCloud is not syncing and freezing the whole system

I added a lot of pictures to my iCloud folder (not iCloud Photos) yesterday, and iCloud has stopped working completely since then. There is no uploading network traffic in the Activity Monitor, no high CPU usage processes related to 'cloud,' and I can't even disable iCloud Drive in the system settings—it freezes there too. Rebooting hasn't helped either.

Thank you very much for your help!