Headhunter causing certain mobs / bosses to not activate when you go near them.

One of the buffs being stolen by headhunter causes mobs that activate when you go near them to not activate.

mobs like the constructs in atziris temple and the devourer boss at the end of trenches for example.

un-equipping headhunter to remove the buffs and re-equipping causes the mobs to activate / spawn as normal.