One of the great mysteries of life I guess, your work has helped me at least.
Meanwhile I'm giving up. The dropbox plugin (either from my own or the one you put above) method hasn't seemed to help any, still can't get it to safe shutdown so I figure I'll set it to run for 30 minutes before it tries to shut down, battery will die well before that but if it's going to do it unsafely either way then may as well try to get it to ride out any outage as long as it can. At least I got monitoring going. Hopefully someone can get a 2.8.0 plugin (or docker maybe?) up and running for unraid.