I wrote this because I got fed up with Teams randomly failing to sync my files documents on O365 resulting in my colleagues either not gettting my updates or vice versa. That said this fix will resolve any of your Office document syncing issues and is not specific to Teams alone.
The Office Document Cache contains the files Office uses to make sure your changes are saved in the cloud. Sometimes when the app fails to sync your documents and you need to reboot or request sender to apply changes again, it’s because your local cache is corrupted. Usually, Office can repair damaged cache files. However usually in my case it ended up remaining corrupted until someone else updated the file or I rebooted the machine.
The solution for this is navigate to close the affected document and navigate to the Office File Cache folder
located at C:\Users\{YOURUSER}\AppData\Local\Office File Cache - assuming Windows is installed on the C:\ drive.
Then select all files with extensions *.FSD and *.FSF and obilerate them i.e. delete them.
Now when you reopen that Teams document it will sync successfully and refresh your local cache.