I appear to need to manually run the "mitra server" command to start the HTTP server on every server restart. I don't know why this is necessary, but it appears to be systemctl that's fucking it up, because it otherwise works.
AFAIK the mitra service file has been properly updated along with the rest of the installation, and it's clearly pointing at the correct executable, but it won't start on its own. Logs show "Main process exited. code=exited, status=2/INVALIDARGUMENT"