Welcome to the DEVONthink forum…
First, reinstallation of this or most any app is not the first step and is unlikely to fix anything.
Second, try quitting DEVONthink, then start again. If that doesn’t clear the issue, then shut-down the Mac and restart.
If that doesn’t clear the issue, report back here with macOS version, DEVONthink version, and the exact (full path) where your database is stored on your Mac.