If you mean “why does his second life never fail to trigger” it’s because it clearly states in his abilities it can’t. It reads “... isn’t affected by ability accuracy reduction”. So. Nothing can make it fail.
Ok. There might be a couple things there. There has been a bug in the past where he keeps degening even below 30%. Don’t know if that’s happening to you. Might be good if you share video. Or. You’ve been using him on a fight with the “Heal Prevention” node. Where he died but stays at 1% Again. Video or pictures would be good to help you identify what’s going on