BG Lethal did not work

I am 2nd, the opponent is 1st with 13 hp. I win the battle and attack face for 15, I should win 1st place but I didn’t. Then he won next battle.

Seems like other people are experiencing this too.

I have a clip but I can’t find a way to upload.

had same issue just right now, opponent got 11 hp , hit it 2 turns at 12, he never dies, then he kills me ^^