what is even killing me?

Im running a block based RF-fire trap chieftain.
POB: https://pobb.in/rd765x9LZ9yp

I have 91%/90% block and spell block with svalinn, 90% ele res and 75 chaos res, immune to ignite,shock,freeze,chill,stun,corrupted blood.
I can AFK kill a guardian but I still die to random packs.
No idea why I keep disappearing in a second to some random rare or magic pack. am I missing something? would appreciate any help you an give.

my guess would be that enemies just hit that hard, it may be auras, it may be ignore armor mods or exposure. Or map mods that severely decreasing defenses.

I know that no matter what you will die once in a while but it feels like my build is very squishy for a 100+ div investment. Is there something I can do to mitigate dmg even more?

Im really no expert on that side of the tree or chieftain firetrap, but I can say for sure that you could use more jewel slots, 2 point jewel slots are always worth taking. There are a quite a few very powerful jewels to chose from, like watchers eye, sublime vision (1 aura).

Never played that build, so can't say much about it.

Just glanced at the pob and it looks solid. Ur Flasks could use an upgrade and maybe the jewels that Andrius said, but other than that u should be tanky enough.

Maybe u are running reduced chance to block mods on some of ur maps with alot of increased modifier effect? Other than that I could only guess that it's maybe some shotgunning when ur block fails, which should be pretty rare tho.

I'd suggest recording ur gameplay and figuring out what type of damage it is that kills u.