Delve exiles seem to hit through lucky block

Ive got a health stack gladiator, with max block and lucky block. For some reason, in deep delve one of the rogue exiles seems to hit me very consistently in spite of this. I cant track which one is doing it because it happens so fast. I tried looking up the abilities and nothing pops up, no debuffs I can see.

Im sure I am missing something, anyone have any thoughts?

Looking at the encounter on the wiki, the only thing to stand out (to me) would be Minara apparently having Minion Instability.

Because the damage from a minion exploding with Minion Instability is secondary damage, Attack and Spell block wouldn't help with it.