What you were expecting to happen, and what actually happened?
Troop with agile trait got hit several times at once (via Sheggra spam). Agile triggered and the troop survived. It showed some remaining health but it did not die after taking further damage (no trait triggering). A closer look (see screenshot below) reveals the troop is actually dead and has 0 health. The game does not end though.
What are the steps to make it happen again?
Spam some skulls against an agile troop. Troop was in the last slot and was the last one to die (might be important).
Do you have any screenshots or video you want to share with us so we can see the problem? Attach them to your post!