NPC Shield wont go under 10%

Hi boys, I am posting this question even here as I am really desperate.

In my own mod, Cosmo is bugged for some reason - his shield won’t go under 10%. No matter what loadout he has, no matter what weapon I fire, it always stops being damaged at 10% of max shield capacity, then it regens back.

I tried different load-outs for him, but nothing helped, and only Cosmo is bugged, other NPCs having the same loadout are fine.
I did not touch any story mission .ini files so I do not understand how the only one NPC may have this issue.

Please I beg you give me some tips because I am losing my hair as there is no reasonable explanation for this.