Vaal beacon not activating, possibly caused by azmeri spirit

Just had a Vaal beacon fail to activate in the burial bog map. I think it had something to do with an azmeri spirit. I was following one at the time and it possessed a rare monster from the beacon, it also turned the rare monster in to a boss encounter (Balbala). Upon killing Balbala and all the monsters around the beacon it failed to activate. I checked around the area to see if I’d missed any monsters but there were none to be found.