forgive me if I'm wrong on this, but I believe there is an issue when you switch the override key. I kept mine as PAUSE and have a few minor issues where the word mute will pop up but everything is still sent to the clients.

Does pressing F12 ever work for you? Have you tried pressing it multiple times to see if it just wasn't taking the first time (stupid, I know but just want to make sure it isn't something simple.)

For the time being you might just want to revert your override key back to PAUSE.