My voids generally always hold agrro without problems. On bossed in entire game i had no issues apart lord incendius in brf(took 10 tries to kill him due to him being higher level 4x). Generally,i wait 5,6 sec before shadow bolt spam but i apply 3x agony ,recklesness asap on all trash mobs. I am full demo aff. I dont ping pong aoe taunt since generally each void holds aggro until trash is dead. I just wait 3,4 sec before hellfire-ing.