Help Lightroom classic 12.3 completely stopped syncing

Hello

I work on a mac with Lightroom classic, lightroom and mobile. Classic is my workhorse.  My catalog contains 500k image and 210k are synced (smart previews ) to the cloud. Everything worked fine for years and updated no trouble on every device wether it came from mobile or classic. 

Since the 17 of april, right after the latest lightroom update, Classic has completely stopped syncing and is constantly in "all synced" mode, what ever is done within classic or through mobile, nothing triggers the sync....

All basics trouble shooting steps have been performed (preferences, uninstall, re install, etc.....)  nothing will trigger classic back to sync 

Nevetheless my adobe cloud continues to populate properly through lightroom and mobile but classic is 5 days behind.... This is a big issue for my worlkload wich is seriuosly in danger now...

I would like to avoid rebuild sync data (been through that ounce and it took weeks) or rebuild the entire cloud data ... it would take more than weeks and I would loose all of my folder strcuture in the cloud; the folders we have to create individualy to nest the collections because classic won't sync collection sets...

Is there somebody out there knowledgeable enough to help me out ? I was in contact for hours with adobe support but they have only radical and destructive solutions ...