Act 6 Titan Boss not Targetable

i cant target the boss. My Compagnion and the Totems have the same problem.

i go into the fight and can target him. After he move to the next position the target get lost and cant get another time. i have to die or wait until he move. But sometimes he dont use the "red ball skill" and dont move. you have to die.
I need 4 runs to finished this. Maybe he get bugged until he get pinned?

I play Tactician on Xbox X.

i have a video. PM me if you need this.