Shock and Horror invisible beam?

Just died a funny death to the Torture Chamber boss Shock and Horror.

Went in like always, a little slow since I didn't play for a few weeks, so she did the beam. Went behind a pillar, beam off, so far nothing special.

Went out again to hit her, and suddenly died in like 2 seconds flat, while nothing at all was visibly
hitting me. No adds, no sparks or totems, and since the beam should be on a 20 second cooldown after I interrupted it (plus, I didn't see anything) it couldn't have been a beam either.

It's not the first time this happened, but it's very very rare, I remember maybe 3 or 4 times in years of playing PoE, and quite a lot of this map, since it's one of my favorites.

Then again, I might have missed something about the boss mechanics. Idk.