There are a lot of prior posts explaining that what DEVONthink does to sync is fundamentally different than other apps, especially those for which syncing is simple. Best to read those past posts to get the “why”. There are also other sites on internet that explains complexity and recent changes Apple made to their sync services, some not quite successful according to those reports.
The new info today from @cgrunenberg about Apple using three third party server vendors (if not more) is interesting and is beginning to help us understand why different people have different experiences. Probably on different sync services with probably no guarantee your computer will connect to same all the time.
If you want sync to work, use a different method. Bonjour and Dropbox (if you need internet method) just works and avoids all this problem re-reporting here.