The 'Switch View Layout' button disappeared from the viewer.

The button was there one second, and gone the next. I know I can find the option in the view menu, but as I use it a lot its annoying. 

I had a 'invalid menu operation'  error a few times last couple of days, which was fixed by deleting the prefs. Maybe it has something to do with it?

Feels like a bug, but maybe I just pressed some button I wasn't aware of?

I'm on the latest version of AE.

Thanks!