Instant deaths

I know these are a part of the game, with more instances occurring with pinnacle bosses.

But I seem to be finding some routine instances of instantly dying to rare mobs. Perhaps they have extremely advantageous mods that I’m missing before hand?

I mostly run magic (2 mod) waystones. And usually not with ones where monsters gain damage.
That said, rares with volatile plants for example seem to not only explode faster but kill me in one hit. I’ve saved several short videos trying to figure it out but haven’t quite noticed anything that stands out.
This is contrary to the volatile plants of rituals which I seem to be able to take several hits from.

I have 36% chaos res, 1500 es 2400hp.

Are there certain things that I should keep an eye out for that = insta death from these rares?

So a 36% Chaos Resist against Volatile Plants is very low. It's all chaos damage so you're taking a ton of that (very high) damage to the face. In addition, as it's Chaos Damage, that ES may as well be 0 (and as it's an AoE and not an Attack, Evasion and Armor have no value). I'd be shocked at surviving two orbs, and one orb is a risk.

These are dangerous on any rare and need to be taken seriously. Attempt to dodge through them whenever able, rather than away, as their chase is eternal until they get close, so any time you can move at and through during a free moment helps clear things up and reduces the times you'll be forced into a bad position between dodging mobs or risking plants going off.

You can have all max res, part of your damage going to minions 4k life and 10k ES and use mind over matter with 2k mana and still get 1 shot popped by a white mob.

The trick is to stay away from everything.