Boss AI - Act 2 - RathBreaker - AI broke and he would only auto attack no abilities used

As Merc I was fighting the Act 2 boss Rathbreaker, after two failed attempts, I tried to bring him to the bottom area.

He came down and charged then reset to the top. I went up to the top to fight him and he would only auto attack, no ranged attack, no slam and no spear barrage from above.

Steps to Reproduce
1. Enter Rathbreaker fight as Merc kill hynea crowd
2. Die twice to the boss (may have no effect to the bug)
3. Third fight, before going up to boss area, shoot the two ads with Galvanic Shards from the bottom of the cliff and kill them (may have no effect to the bug)
4. Move to the top area and start the fight
5. Run back down the slope and try to get the boss to come down and charge you
6. He will reset and walk back up to the top
7. Wait for him to return to start positon then follow him up
8. Start fight and observe what abilities he uses

Result: Rathbreaker only auto attacks and uses no abilities

Expected Result: pulling him from boss area or reset does not effect Rathbreaker AI

Class: Merc lvl 18
Weapon: Crossbow
Main abilities: Flash Grenades - Explosive Grenades - Galvanic Shards