Speaker symbol mutes, impossible to unmute

Hello all,

when I stream a video or audio, a speaker symbol appears at the "rider" on top of the tab. (Sorry, I don't know the english term.) When I left-click the speaker symbol, the sound of this tab is muted. But it is a different mute function than the one that is listed in the menu that opens by right click on the tab rider. Clicking the speaker symbol again doesn't bring back the sound. Whatever I try, the sound doesn't come back. I can only close the tab and re-open it to get the sound, but there must be a more elegant way.

I forgot to mention, that the problem I described only appears when the tab is pinned.