Explodes nearby corpses damage might be miscalculating

I played level 88 Warbringer on HC Rise of the Abyss and got one-shot by an explosion near corpses. This should be the mod causing it, as there were no monsters around me when I died, and I saw a rare monster with a modifier at the far edge of the scene.

I have 3,015 life and more than 20k armor (more than 90% physical reduction cap thanks to all the shield mods and the Escape Jade passive), with all the armor applying to elemental damage to reach over 100%. I also have 75% elemental resist and 67% chaos resist (kinda tanky, though). Still, I was one-shot by something I couldn't see.

The problem might be some monster that explodes (in my case, a rare Strider of the Abyss) that bypasses all damage reduction. I tested the damage with all armor and evasion 0 character, just 75% elemental resistance, and it still dealt around 3-4k damage—similar to my warrior, who had all that damage reduction but got one-shot by it.

If it's not too much trouble, please review some damage calculations for that mod or analyze the invisible explosion I've never encountered before. Thank you.