Here is how it works. That new Kurotsuchi (only exists in CN as of right now) will put a debuff on 2 random ninjas at the start of the battle that will prevent those ninjas from receiving buffs or shields. That debuff can't be immune to or dispelled. You probably noticed that Tsunade poweres herself up at the start of battle. That things that she does to herself is the immunity-to-death-buff that is unremovable. However if Kurotsuchi lands her debuff on Tsunade BEFORE Tsunade makes herself immune to death then Tsunade can't even make herself immune to death because immunity to death that she applies on herself is counted as buff and therefore can die round 1. Of course the chance of that happening is very slim but that is exactly what happened in the video you saw when you look closely.