The plugin stores all of its data in your browser profile, so it doesn’t need to be online to work (although of course you need to be on line to view suttas unless you have the site saved for offline use… Which actually is a good case for the plugin since I don’t think even the quick results I showed above in the built in search will work offline, although I’m not sure).
It would be great if you could post about this when it happens in the search bug thread: SuttaCentral Search Bugs 🪰 Hopefully we can figure out your problem there.