As a previous poster said there was nothing in patchnotes so either you did something wrong on interrupt or he is really bugged. One way or another tank should be able to live through his channel and if anyone else grabs aggro on this fight its tanks fault since he has enough taunts to never loose it even if there is any kind of threat drop.
Did you skip my entire first post?
You cannot interrupt this boss anymore, and he drops threat as soon as he knocks you back, and because you cant interrupt, your taunt is pointless while he's channeling into other party members.
Edit: Its not about anyone taking agro off you, as a tank, its about the boss dropping it and randomly targetting party members with the uninterruptable channel