I actually think this is the issue that both of us and many other people are having, and I’m expecting them to perhaps merge us into it:
The only reason I commented on your ticket is because it was the only one I saw open at the time related to the Last.fm login, but this does appear to be a widespread issue that is not specific to either of us (which is both good and bad). 
We’ve merged some additional reports from the last week into the tracking thread for this issue. Please stand by as we continue to investigate this issue on the backend.
Same login issue with Last.fm in Roon. I noticed that songs scrobbling on Roon were being duplicated on the Last.fm site so logged out of Last.fm in Roon settings and disconnected Roon on Last.fm website account. I also rebooted Roon server before logging back into Last.fm - I now have error message “Failed to login to Last.fm.”
This also happened to me yesterday after a minor power surge that knocked out my internet for a bit. Once it was back up and I could access Roon again on the network, it was saying there was an error with Last.fm authentication.
I’ve tried repeatedly, restarted my ROCK repeatedly, and just get “Failed to log into Last.fm”
My Last.fm credentials are fine.
I have to add my name to the list who cannot connect to last.fm either, sadly.
I have also been having the same issue with connecting from Roon to last.fm. I get a “Failed to log in to Last.fm” message when trying to connect on the Services screen. Username and password are correct. I’ve removed Roon application from within Last.fm, restarted Roon server, but still getting the error.
Looks like there is a fix on the way for this; hoping I will now get a notification when it’s available.
I am in the same boat. I recently logged into Last.fm for the first time in a while and had to change my password. Since then, I’ve logged out in Roon settings and also disconnected Roon in the Last.fm application settings. Still getting a “failed to log into last.fm”. I can log into last.fm with that same username and (new) password.
I have the issue as well. Since last week, I’ve been experiencing a “Failed to log in to Last.fm” when attempting to log into Last.fm through Roon. Last.fm works fine with Qobuz alone. I’ve also tried re-installing Roon and tried creating a different profile in Roon. Please find a solution, soon.
I’m also unable to login to last fm on a new roon install. I did see the login as an active session on the lastfm website so the login attempt seems to at least reach them, and the authentication is successful on their side.
For Mac OS users:
I just downloaded Scrobble from Bretth18 at Github. Little app that scrobbles Roon and Apple Music on my Mac mini. It’s the first app that scrobbles both with no problems. It also scrobbles from Spotify or any other streaming service. Glad my music is scrobbled again.
· None of the above quite fits
· None of these quite match
· Login issue with Last.fm in Roon. I noticed that songs scrobbling on Roon were being duplicated on the Last.fm site so logged out of Last.fm in Roon settings and disconnected Roon on Last.fm website account. I also rebooted Roon server before logging back into Last.fm - I now have error message “Failed to login to Last.fm.”
· British Telecomm BT Smart Hub 2; Netgear MS305 switch; Cambridge Audio CXN (V2); Roon (Rock) server on ASUS NUC 13 Pro Mini PC. There is no VPN and is wired throughout.
Roon Labs is aware and investigating - see:
· None of the above quite fits
· None of these quite match
· I can't seem to reconnect to Last.FM. Connection had be fine but today it prompted me to re-login and I keep getting a login failed message. Logging into Last.FM with my email and the correct password
· Using TP-Link Deco mesh network. Worked fine previously
Hello @jeff.declerck and welcome to the forum.
Roon Labs is aware and investigating - see: