layer 10 Bat Swarm Issue

yesterday and today i had the same issue.
I am finishing layer 10, putting all my bats in the setup, i click run and then nothing seems to die or to be shown on screen as dead, but when i go to my troop overview, all bats are gone, it happened a few times already.
either is a hidden message of the troops that died and it's not displayed or they just disappear in layer 10 just by default.

I had to refresh the game and wait a bit and all the bats are back.
i'm not sure if it's a bug or just a visual bug, but still a bit scary