Having the same problem, only streamed songs can be scrobbled, I'm using the connect to Spotify app from the last.fm site. The Spofity add-on doesn't seem to function at all atm, but I think that's an issue with last.fm and not Spotify.
edit: I suggest upvoting this topic, maybe they'll see it faster then.
edit²: Seems like it's a problem with last.fm, check their last.fm status Twitter, they themselves said that Local File scrobbling is not possible atm.
I have the same issue. First my stuff stopped scrobbling all together, but when i clicked on the new connection in Last.fms applications for Spotify scrobbling, i fixed it. However, now it’s not scrobbling Local files, no matter what I try. And i can’t remove that connection anymore, because then won’t scrobble again, I already tested that.
The issue is not with last:fm. All other scrobblers work perfectly fine.
Scrobbling is currently broken on all Spotify versions. I'm assuming they use a plug n' play component for connecting to the Last.fm API, that they broke at some point last week; the broken functionality was rolled out in waves. Windows Spotify scrobbling broke late last week, iOS Spotify scrobbling was broken by an update two days ago. If we're lucky, they'll fix the problem soon so we can go back to scrobbling normally.