help: stun tower doesn't stun

Hi,
I'm running blight in T16 toxic sewer with my RF chieftain, and blight monsters are not being stunned.
I made sure there is no bad modifier on my maps (cannot stun, cannot change action speed), to use chilling tower when monster are immune to seismic, and it seems that no red altar stun.
What could it be?
Thx

I think it's enemies with energy shield. Particularly the map mod: Monsters gain X% of maximum life as extra maximum energy shield. They'll have 50% stun avoidance w/ ES.

Here's a vid of a map w/ life as ES and you'll see them being stunned for a bit, then just walk right through it all.

https://www.youtube.com/watch?v=ZxeJuRdPwH4