I used matrix a while ago and join the matrix-dev channel at that time, which seems to be no longer in use. I can try leaving it but I receive an error
Failed to leave room
@Alexendoo:matrix.org not in room !DYgXKezaHgMbiPMzjX:matrix.org.

Oddly, the URL for the page is https://riot.im/app/#/room/#matrix-dev:sputnik-messenger.com
+ submitted debug logs
Looks like the server and Riot disagree on whether or not you're in the room - try going to Settings then under Help & Support press "Clear Cache and Reload". It should resolve the issue.
That seems to have worked, thanks. I was kicked for inactivity

I was able to forget the channel afterwards. Not sure if there's a bug for that somewhere but I'll close this one in any case, since I'm not confident I could reproduce it again without a time machine
@turt2live @Alexendoo Hello! I experienced the same thing. The channel was stuck and I wasn't able to leave it. Found this issue via Google, cleared my cached and then got a message telling me that I got kicked because of inactivity. After that, I was able to join again. From a user experience point of view, this seems to be a bug.