Ok i got the same problem again in special intel mission with "all enemies are heavy armored" tag. 

This time with a heavy bolter and Chaos Spawn enemy. I can kill all the other enemies in same mission : gobler, renegade gunner, black legion marine etc. without using armor piercing skill even when they have heavy armor tag. 

Chaos Spawn can take full clip in the face with a heavy bolter and not take single point of damage (full auto skill). Armor piercing skill damages them normally without problem.

So there is a bug with Chaos Spawn enemy and intel missions with "all enemies are heavy armored".

Yeah maybe there was some other damage reductions like 80% resistance to damage for 3 sec im not sure anymore. 

I tested this more ( i did run more black legion maps with lvl82 card and enemy defensive cards and i got "all enemies are heavy armored", but those maps i had no problem to damage and kill them with all plasma cannon skills.) 

So maybe it was onetime fluke or is special intel mission tag "all enemies are heavy armored" making enemies immune to all but armor piercing skills?

Another questions i have would it be possible to give user to option to change ( when using xbox controller in PC) item activation from A (skill) button to X (reload) button? it is really annoying when your character starts to run to open grenade/health/quest objective when the are enemies around instead continue to shoot using A button skill.