Sync error

Joplin 1.78 running on Android 9, Win 10 Enterprise and a second Win 10 Enterprise machine. Sync via Dropbox. All is well on 1 + 2, but on 3 only one notebook (the built-in “Welcome”-thing) gets synced (well, it’s built in, so …). A large part of the notes from the other notebooks gets dumped into the root folder (I guess that is what having lots of notes with tags outside any notebooks means.)
Logfile output includes the following:
2020-01-27 23:54:38: "Operations completed: "
2020-01-27 23:54:38: “createRemote: 1”
2020-01-27 23:54:38: “fetchingTotal: 2”
2020-01-27 23:54:39: “fetchingProcessed: 2”
2020-01-27 23:54:39: “Total folders: 1”
2020-01-27 23:54:39: “Total notes: 270”
2020-01-27 23:54:39: “Total resources: 3”

Actually there are about ten folders with about 2000 notes, which just don’t get added (though new deletions and additions apparently do get synced as the excerpt from the output shows).