“Adding Previews” over and over

I sync 6 databases to DEVONthink to Go on an iPad Pro. The content of those databases changes by maybe 5 documents a day, and usually fewer. Yet every time I open DEVONthink to Go, it starts a long slow count down for “adding previews” to the several thousand items in the databases. “Adding previews” never ends unless I leave DEVONthink to Go open for 45 minutes to an hour and don’t use the iPad for anything else.

Why?

When all previews are created and saved the “creating preview” process should calm down. The images are stored with the records and DEVONthink To Go does (should) not regenerate them unless the files have changed.

But that’s not what happens. Even when no files change “creating previews” kicks off and I have to leave the iPad sitting for a long time while the process goes on and on. These databases in DEVONthink to Go are old, synced a long time ago, and should need no new previews.

And when it’s over and you don’t sync, it’s okay or does it begin anew even when you do not sync anything? Just exploring possible causes.