I often migrate between 3 different computers and have Butterdocs on each. For each install, it asks me to choose a Backup folder, so I use a dedicated folder on my Google Drive. The problem is none of the installs can share the same folder. (Ostensibly, I understand why because it would seem to be a version control nightmare for backup files.) So, I have like 3 nested backup folders, all for the same story. This seems like it could problematic in the event that I would actually require a backup - do I have to restore on the machine where I did the most recent work, etc? I don’r know how or if this can be resolved, but it is something to consider, I guess.

They should be able to share the same folder, by what mechanism is that made impossible for you? The backups are just markdown, you can open them from any machine.
I have butter docs on a mac min, windows laptop, mac air, & desktop (this used the least; the desktop). I ran into the issue of selecting the same backup folder using dropbox and ButterDoc just gave a generic error. The problem was only fixed when I created a new folder and didn’t use one attahced to exsiting folder for a diffrent PC/Mac.
I use another software called Lattics in the same way and it doesn’t have this issue.
You’ll see in the screen shots. In fact, my back up for the Mac Mini was set ‘ButterDocs MacMini’. When I selected a diffrent folder (used by ButterDocs on a diffrent computer) the error showed up.