Copper Citadel Phase 1 Boss damages through Asala Shield

Here the situation:

I attempted Copper Citadel boss in Hardcore with my Minion Infernalist, I noticed it's too strong for me and asked a friend to help me.
We damaged him to the Wind/Shield mechanic in P1, I was standing in the shield but still got damaged and died almost immediatly + I had a Omen of Resurgence active but it didn't pop when I got low.

https://imgur.com/a/heZO1A7
I took the screenshot right after respawn.

I hope this helps finding a bug.