I don’t use Last.FM myself, but perhaps see if the information mentioned in this link might assist you;

https://support.sonos.com/s/article/803

Ensure your Spotify account is linked etc.

I’ve done all of that and it syncs when I stop using my sonos speakers and play on my phone/laptop/etc for a moment, it’s just odd it doesn’t sync while playing on the sonos. 

This is what the support document mentions…

………..

When does Sonos Scrobble?
In order to be scrobbled, a track must play for 240 seconds or halfway through, whichever comes first. It must also have a track length of 30 seconds or more. Once these conditions have been met, the track is scrobbled when playback completes or the track is changed by the user.

…………

If that’s not what is happening, then perhaps within 20 minutes of seeing the issue, submit a Sonos diagnostic report from the ‘Settings/Support’ area of the Sonos App.

Make a note of the reference generated and then, when available, contact/chat to Sonos Support Staff about the matter via this LINK and see what they can suggest to resolve the matter.

I have the exact same problem! Whenever I play music on Spotify from desktop/mobile speakers, last.fm scrobbles the tracks perfectly. Without fail, when I swap to Sonos speakers, the scrobbling immediately stops, and won’t restart until I swap back.

Upon swapping away from Sonos, last.fm will (temperamentally) push all the missing scrobbles for the relevant time period through to last.fm, sometimes immediately, sometimes after 10-60 minutes or longer, and sometimes not at all.

From numerous comments I can see on reddit, last.fm support community, last.fm discord, and this Sonos community across the past 12-24 months, this is clearly not an isolated issue.

When playing from Spotify to Sonos, Sonos does not speak to last.fm properly. I’m not sure if Spotify is also part of the problem, but I’m tempted to think it isn’t... because scrobbling works perfectly from Spotify to any other speaker system. I think it’s the Sonos app that’s the issue, and how it connects with the last.fm service.

I have the same problem. How much longer before you acknowledge and fix it Sonos?

Exact the same issue for me, since I own my Sonos system (end of 2021). I always connect via Airplay and not via Spotify Connect and/or the Sonos App because nothing is scrobbled. Only if I switch to my mobile phone or else via Airplay everything I played directly through Sonos is scrobbled at once. However, only the last 50 tracks are cached by the system, if you play more it’s lost.

This issue has been mentioned countless times in this forum and it has never been fixed. The Last.fm service in Sonos is useless as it’s not working. Fact.