It seems that latest 68 beta works fine with enabled synchronisation.

The same problem: https://forums.opera.com/topic/38766/opera-sync-in-browser-does-not-work-anymore-and-then-it-freezes

The same problem on Opera Stable 67.0.3575.79 and Win 10.

By the way two days ago I had the same problem on Mac OS but I have solved the problem by updating to a new version (after it appeared). I made all operations very quickly... (:

Thanks! ):

How can I change site icons at the new Start Page to site preview like in the old version?