I’m running Nephalem Rifts to collect keystones for Greater Rifts, and I just killed Cold Snap. An instant later, one of my own Arcane Hydras kills me:
https://drive.google.com/file/d/1DbqG7FUn95E1O81AMBp2iNYGwtk-yu99/view?usp=sharing
Has this happened to anyone else before?
Embedding that for you…
I’ve not seen any other reports of this.
Only thing I can think of is were there any Dune Dervishes or Sand Dwellers on the map? These mobs can reflect projectiles. You have your Hydra runed so they cast arcane orbs. I don’t know if that’d be classed as a projectile or not but, if so, it could have been your hydra’s orb that killed you.
[ EDIT ]
Easy way to test this is to go looking for the Keywarden in Act II, as it’s a boss version of a Dervish. Drop some Hydras next to it, and see if their orbs come back to you.