Tormented Durial.. bug?

So, last night with another player, we attempted Torm Durial… summoned him and started the fight… now we got to the part where Durial burrows underground… no minions were out, there is no poison or anything on the ground… yet we both died almost at the same time. I can’t speak for my partner, but I was at full health.

Why?

Ok, let’s try that again… my partner dies almost immediately and Durial hasn’t even popped up yet… I fight him, get his health down to half way… he then burrows underground… again, no minions or poison… then I die again and with full health

What?

Third attempt… Durial is popping up (not fully out, no health bar) we both die instantly!

What’s going on? Absolute waste of our mats to summon him and our time, if we can just be instantly killed, when nothing is going on.