You may want to check, if you haven’t already, the WD Sync help file to see what options there are available for skipping/ignoring specific files. I never used WD Sync (beyond a quick test of the software) due to these kinds of issues with it.
As a troubleshooting step (if you haven’t tried already), if you know which files WD Sync is failing to sync, move those files to another location that isn’t being monitored by WD Sync and see if WD Sync clears the sync error(s). Then move the files back and see if WD Sync will sync the files correctly.
Edit to add: Also just remembered this discussion on WD Sync exclusion file from 2015 that one could, I assume, still use to force exclusions of certain files from being synced by WD Sync. This could be another way to deal with problematic files that hang the WD Sync program.
