Dropbox app is inconsistently syncing some folders but not others

I have a WDMyCloud2100 (2 Bay) running the Drop Box App and using Selective Sync to sync only part of the Dropbox account to the MyCloud unit.

The system has worked fine until last week. I am noticing that some new folders and files on the MyCloud do not sync to DB, though files in other folders do.

I have
*unlinked and relinked the App
*uninstalled and reinstalled the app.
*created new files on the Dropbox side which also fail to sync (ie. it’s a two way problem)
*confirmed that none of the affected folders or files have invalid properties as per Dropbox instructions.