That was a great help — although, for me the sorter folder was not inside ~/Library/Application Support/DEVONthink Pro 2/ but rather its own location in the Application Support folder at ~/Library/Application Support/DEVONthink Sorter/. Inside that was a folder “Global Inbox” and inside that a folder “current”. I trashed these last two, then restarted, and found a new “Global Inbox” but no subfolder “current”.
The problem seems to be fixed for now. Perhaps my solution is temporary… we’ll see! Thanks for pointing me in the right direction.