Lightroom Classic syncing stuck

Hello,

My Lightroom Classic is stuck with 239 photos to sync. I have about 14,800 syned and it has been working perfectlyh until recently. These are the thjngs I've tried:

1. I've updated to latest version 11.4
2.  I've deleted the Sync.lrdata folder and waited for it to stabilise.
3. I've waited on the Preferences->Sync Activity for over 5 minutes and it shows nothing.
4. Every now and then it shows a few and then they clear. As far as I can tell, all the nes that show are already synced.
5. It seems the ones not synced are distributed across my library rather than being the last 239 photos. The last 212 photos are not synced but the other 27 are distributed across my library.

Any help most appreciated. 

Thank you