In the Mogu’shan Vaults, I had just finished killing Elegon, where Cho used the control panel.
Then I went back to the Will of the Emperor area, killed the three mobs, then (so I thought) I clicked on the control panel then went down to the lower area.
But nothing happened.
So, I went back to the control panel, where Cho was standing, and it appeared shut.
I thought perhaps I had forgotten to activate it, so, I clicked on it again. It opened, then shut again immediately. I tried going to the lower level again, but nothing happened. The mobs from the alcoves didn’t spawn. Realizing I wouldn’t get to do this last fight, I finally left.
Not sure when I did wrong. The raid was set for 25-man mythic.
Perhaps I was in such a rush to get back there, I should have waited for Cho to show up before I used the control panel. But really no idea what I did wrong.