"Plugins have been updated-restart required" won't go away, Triode Spotify plugin MIA

I just upgraded my Mac to Yosemite, and LMS to 7.7.4, and my previously working Triode Spotify plugin stopped working. In my attempt to fix it, I (among other things) unchecked it on the plugins page, and it has now disappeared completely. More troubling, LMS now constantly shows the message "Plugins have been updated - restart required", and whenever I go to the Settings - Plugins page I am immediately hit with the message "Changes will take place at the next application restart. Please click here to restart the server now." Yet stopping and restarting LMS doesn't fix the problem, these messages remain and the Triode plugin remains missing. I even tried adding Triode's repository manually, to the Plugins page, all his apps except for Spotify are showing up. I've also run cleanup to clean the cache folder from "LMS - Advanced" in the Mac's System Preferences (but I didn't click "Delete preference files" as I'm unsure what other damage that might do?) I've rebooted the Mac as well, and have tried reinstalling LMS 7.7.4 (without first deleting it, not sure how to do that or again, what settings I might lose in the process).

The official Spotify plugin is misbehaving too, I can search for music, but as soon as I try to play, my Squeezebox Classic shows the song but no sound comes out, and on the web interface it acts like its playing the first song on an album for 2 seconds then skips to another track way further down the list (this started happening today even before I upgraded my Mac and LMS, so something may have already been corrupted even before the upgrade).

Clearly, something is stuck somewhere relative to plugins, but I don't know what?