I was in hardcore helltide t4 and my hellborne just appeared. I was fortified with capped armor & all resistances. I had just finished changing equipment and aspects, so I know they were good. I did not use a mindcage. I have felt in both hardcore and softcore that at times there has been damage reflected back at us, like the enemy has thorns or some sort of reflect damage glitch. I was using a modified dust devil build with tons of dust devils around me at the time. My toon, lvl 100 RockNutJr died via Unknown Killer in the fallen characters screen. I was so surprised that I missed the 1 min limit to capture the footage, it only shows after the death which can be provided. The death felt out of place and was shocking with no explanation. Nothing should have killed me instantly in helltide.
Update:
Another barb, lvl 88, succumbed to unknown killer. This time I was in a group and they said the game chat showed “player name was killed by player name”. Apparent suicide. I was in shock again and missed the capture window. I would love to know what causes this to better defend from my hardcore character dying by suicide/unknown killer. Not fun at all.