Simulacrum: can't move to the next wave

The video recording explains everything...
https://drive.google.com/file/d/1M_B1vo4CK_jAxG3ebtD0R4qlhV5cP4vD/view?usp=sharing

Killed Kosis in Simulacrum.
Kosis' health bar and himself didn't disappear.
Cleared the wave but the health bar and Kosis still in the game.
Next wave button appearerd but is not click-able.