Clips from streams.

the mobs behave this way because they can kill a heavily armored, expensive unit; the same applies to ifrits. Don't cast Wave of Death right away, and it will be fine.

Added 10 minutes later

2:16:00 - the same story. Does anyone know why the mobs behave this way?
https://vk.com/helllight111?z=video-110795600_456239580%2Fcc39de66f2eaa0b9ac%2Fpl_wall_-110795600

and this is a classic; you need to first attack them with ranged units after the first wall.