Thanks, Jim. Appreciate the reply. Since my last post, some digging around revealed that there were some pending files trying to sync that seemed corrupted or missing, so I deleted those thinking that might kick start the sync process again (which I also found to have stopped approx two weeks ago).
When that didn’t work, I archived a full copy of the database in question for safekeeping (it’s one I’ve been using for over ten years) and set to work cleaning and rebuilding. That didn’t seem to work either.
I then set up a new syncstore using iCloud to do some testing. My thinking was that a fresh start ought to reveal similar problems to the dropbox syncstore. The good news is that the iCloud syncstore seems to work just fine: I’m getting stable and fast syncing between DTTG and DT3 on the problematic database.
So it was not all in vain, I’ll take what you’ve written above and play around this weekend with the problematic database on dropbox. I’ve still got the dropbox syncstore holding quite a few other mission-critical databases. Those seem fine from what I can tell, but hopefully this thread will be useful for anyone else going forward.
Trust you had a relaxing (and well earned) holiday break, old friend. 2019 was a big year for you folks.