Good Evening (at the time of writing), hope everything is well.

When you select the perk which reduces damage, it turns the wall/gate invincible with "Fortified Walls" (or any/most structures, when selecting the perk "Iron Curtain").
It seems to be an issue with the way the code is set up, where it ends up healing part of the damage suffered, instead of reducing the damage instance, something among these lines.
I'm not really into programming, but maybe doing something where it checks the structure HP and compare it with the damage, and if it would to or below 0 it is destroyed instead of healing?

I noticed this when playing with a lot of mods, including rampant, and for some reason even with 50% evolution, there was almost no issues with biters although my defenses where mostly shotgun turrets and walls only.

Hope you are still active.