I see a lot of people on here weighing different sync solutions for DEVONthink, or struggling with some of the sync configuration when it comes to using iCloud sync.
Jim from DEVONtechnologies just posted some tips for setting up iCloud syncing that should hopefully help anyone struggling with this process. Worth checking out:
https://forum.devontechnologies.com/viewtopic.php?f=2&t=26490