Uploading items to iCloud never ending (for weeks)
Happened to me as well, here is what I did:


Back up all items in the Documents and Desktop folders (or wherever you are backing up your files)
Open up System Preferences
Click on iCloud
Click on Options next to iCloud Drive
If Desktop and Document Folders is disabled, enable it
If enabled, disable it.
Uncheck the Optimize Mac Storage and click Done
Redo the opposite of steps 5-7 to re-enable iCloud
Move all Documents and Desktop items back to their respective area.


It is helpful to note if you are experiencing sync issues in any of the other categories in iCloud Drive, try disabling them and then re-enabling them.