u can line of sight the chaos bolts kanrethad casts. or use demonic teleport. the best advice id say would be to always remember to put kanreth as your focus. that way u can see him casting his 5 second chaos bolt. or the cataclysm and have your pit lord interrupt it. if ur still having trouble just try for some better gear, warm sun flasks, even prepotting or maybe drums of rage too for 35% lust.