Lightning warp unable to cast in Zahmir boss fight

Abyss spawned deep in Zahmir t15 map boss arena, had to bait each abyssal enemy out of boss room to kill. Finally cleared them all, went to fight boss and my lightning warp would spend mana but not cast or deal damage. I tried placing it on a different keybinding, but it was still unable to deal damage.

Image once I died:
https://gyazo.com/7628cdc1175ee08c7f47bb6c9f5951a4