@Halloran Strange. Is the Spotify version a very old one? You should also uninstall all Spotify plugins, including Connect if you still have that. Always restart Volumio after uninstall (if you eventually get that far!) and before re-installing.
Still, if it’s not too much bother, a clean install will clear this up.
@SimonE On this Pi, the Spotify plugin was probably originally installed quite a long time ago. But since it seems only half installed, I can’t tell the version. And I’ve restarted a million times in this process.
At the end of the day, doing a re-image is probably a good idea anyway. I don’t have much in the way of customization (just the NAS config) anyway.