Thanks. I cleaned the syncstore earlier, but not changed name. How would I do that?
You can’t. You need to make a new sync store but use a new name. And you can even try isolating the problematic database to the new sync location.
I should have said todays event is with a different database than the one earlier in the thread. Perhaps I should do the same for that database.
So is the process that I delete the existing CloudKit Sync location? Then create a new one. I have never noticed (or looked for) a place to give it a name.
CloudKit? A buunch of the discussion in theis thread is about Dropbox. 
The referenced files are all on Dropbox.
The DT sync location is CloudKit and Bonjour.
In the OP I said that initially I was only using Bonjour for sync and that is when the first “couldn’t upload” message occurred. Then I added CloudKit and DTTG sync’d it, hence thread title.