I’m having a similar problem. Toggle Full Screen (Ctrl-tilde) only works on my laptop monitor, regardless of which Playback monitor I have checked, or whether I have Enable Transmit selected.
I think the issue has to do with the screen setup. I have my menubar on an external monitor, not on my laptop monitor. However, if I move the menubar back onto my laptop monitor, Enable Transmit works. It doesn’t seem to have anything to do with Toggle Full Screen (Ctrl-tilde).
Does anyone know of a way to view full screen on an external that has a menubar?