This happens to me too. I think the issue is that you’re following a hashtag that the muted user used and it’s somehow bypassing the mute
@ 
nostr:npub1yzvxlwp7wawed5vgefwfmugvumtp8c8t0etk3g8sky4n0ndvyxesnxrf8q I am trying to mute this user, so he does not show up for example when I browser the #asknostr feed. Check this screenshot. I have the ability to "unmute user".. which suggests I have already muted him, yet he is still showing up in my feed. Is that expected behavior or not expected behavior?
Discussion
Lol, I remember people were encountering the exact same bug... on a completely different website.
It seems like a universal mistake. It's destiny.