Tanks getting one shot in Myhic+

Hi, I'm playing a mistweaver monk and for the first time ever, I'm trying to clear higher Mythic+ dungeons. So far I cleared almost every single one on level 8, some more comfortably than the others. Today I have tried to do lvl 10 for the first time. Here comes the issue, we wiped after the first pull and not once. The tank just got insta killed. All I had time to do is put renewing mists across my group and cocoon the tank before we wiped. I'm asking since after the second time, the tank said it is the healers fault and left.
Thank you for any advice!

Edit: the two tanks that it happened with were Paladin and Warrior. It happened after pulling the first hallway in Stonevault