The State of iCloud
The upcoming macOS Catalina as well as iOS 13 were about to bring many changes to how the directories on the hard drive are structured as well as to how iCloud is integrated into the file system. For the late DEVONthink 3 betas we had spent quite some time on updating our iCloud handling accordingly.
However, there were massive problems with these changes and while things improved from one Catalina and iOS 13 beta to the next Apple didn't manage to fix them completely. Finally, Apple rolled back all changes and, presumably, prepares for reintroducing them later.
You can read more about recent iCloud problems on Craig Hockenberry's blog, the developer of Twitterrific and other great apps.
If you rely on iCloud, e.g., for synchronizing your DEVONthink databases, we recommend to not use the macOS Catalina and iOS 13 betas and check for news about the state of iCloud before upgrading your systems. Daring Fireball's John Gruber recommends to even wait for iOS 13.1.