It is the second time this has now happend but it is rare and it didn't happen exactly like before so I don't know how you can replicate this however the bug is if you somehow get the character to exactly 0hp they still live. The first time this happened was maybe a month ago in some SA (yagura I belive) and I was able to still use sasuke when it showed he had 0hp. I don't remember if he died the round after or not.
The second time was recently in space time although this was just an animation issue. After I killed someones kimimaru he glitched out and kept standing there and moving like usual but you couldn't select him, or hover over him to see his hp and my chars just run through him as if he wasn't there so just some animation issue. There's no way I would be able to replicate this as this is too rng based on dmg so I can't gather more data.