The announcer npc who starts the roleplay which eventually triggers the bosses to spawn doesn’t appear properly after you kill the Yeti boss. I somehow managed got him to appear for the second and third trial after waiting for an entire day until server reset but eventually as you reach the faction champions encounter, he refuses to appear and it becomes impossible to continue. Tirion performs his speech, the gate behind you closes as if the encounter had started and you are now physically locked inside the instance.
I don’t know about the heroic Grand trial version of the raid because I am not allowed to enter the instance without completing the normal difficulty one first, which has been impossible for quite some time now.
It might or might not have something to do with playing on Allied Race characters.