Maybe solution? (idk, that was my case)

So, if you have that problem and pinned tabs, go to pinned tab #8 unmute/mute button - works
next
I Try go to 9 works, but Changing tab to #10+ dont and if you go back to #9 mute button again is broken
but pinned 1-8 are working
non pinned tabs are still broken so... (that sucks)
And that works only whit "workspace" #1 (idk why)

I hope I helped you(Opera) find a solution/cause of this bug