Citadel bosses one-shotting when they really shouldn't be?

I noticed this last season, and it's still happening this season, but citadel bosses (which I'm pretty sure have no one-shot mechanics) are one-shotting insanely tanky min-maxed characters, and there's no indication of what ability killed them.

This season I'm running a bear with 13k armor, 2400+ life, a little (200) ES, and 2k+ mana, with mind over matter, and about 140% armor applies to elemental damage. I ran a very tame T15 map on Iron Citadel, got to the boss, leapt onto him and immediately as I was about to land I went from full health, ES, and mana to dead instantly.

Last season I was running a chaos inoculation invoker with some 12k ES with meditate up, and I would regularly get one-shot by citadel bosses.

In both instances, I can face tank max Xesht's hand drop and multiple fist slams, but these random bosses somehow one-shot me regularly.

I also noticed the Geonor citadel boss "ice beams from the sky" attack is doing crazy high damage. Died on my first 2 attempts getting 1 or 2-shot with no damage mods on map (3.2k life, 1.3k ES, capped res and Avatar of Evolution). Always froze me in 1 hit as well despite never having issues with freeze otherwise.

A bit overtuned for an attack that difficult to reliably dodge.