NESSA Boss Fight bug: never dies at 25%

Hi,
I've been stucked at the boss fight nessa on map tier 10 with maeve watching: the life of nessa never goes down after 25% life.I tried to move boss in center of map (in case it was a position bug) but still never dies. I have made screenshots showing the length of the fight and the same life despite all the minions attacking if needed. I tried to leave and come back on a portal, still don't die. The boss is not stuck, it attacks me and my minions. Maevan casts are working "protect" "grasp"...
Thanks for correcting for others!