Following this helped to some degree. I disabled note history on all devices and my notebooks are now syncing successfully from the Linux client to one of the Android devices. (Thank you for getting me this far!)
Excellent! That means that the notes and notebooks are on the server (which is what much of the debugging information above would have been for 
).
(The debug report feature on Joplin server, as originally planned, seems similar to a feature that seems to have been removed for causing database lockups on the server).
Moreover, all devices are still fetching a lot of items during the sync and reporting a lot of revisions in the sync status, despite disabling note history on all of them and notes reporting "This note has no history" when I inspect them individually.
I'm unsure why the revisions are still encrypted, since I've entered the master key for my database and it's not prompting me for any further keys.
Here are a few possibilities:
- These statements are from before the revisions were decrypted.
- There's a bug in how revisions are being deleted!
- Many of the revisions are related to resources, which, reportedly, can take several days to be removed after all notes they were linked to have been deleted.
What I find odd is that I couldn't reproduce this on my second device. It is still stuck in the state I described in my second post here.
Another user had success with upgrading to the prerelease version of Joplin:
If you would like to try the prerelease, the Android prerelease can be downloaded from GitHub (or an unofficial version can be downloaded from F-Droid).
According to the Joplin Release Cycle, the current prerelease is in feature freeze and should become stable in a few weeks.