Earlier today I completed all Normal raid bosses in Ny’alotha on my character Paulusxii-Frostmourne, up to and including Carapace of N’zoth and had a few attempts on N’zoth the Corruptor when the raid was disbanded. Several hours later I have attempted to continue on and when I enter the raid I am teleported into an empty N’zoth encounter room.
I have checked my raid info and it shows all bosses up to N’zoth defeated with only N’zoth available. There is npc text between Mother, The Keeper and Wrathion regarding the azerite focus beam and how we have only one shot.
The room is empty with only a portal on the opposite side of the room from my spawn point that takes you back out to Pandaria.