He should have a -6 debuff instead of a -12 one. If not, report it as a bug and I'll look into it.

I'll wait around to see if anyone else has the issue before I do as there could be something else (another mod perhaps) that conflicts with it or something.

Thanks for the response!

Have the same problem. My pawn has depressive, chem.fach, pyro, too smart traits at the same time. Moreover, my colony has no more positive mood offset, because of wealth. So, this pawn is always walking trouble. And three trait treatments give him +6% mental break threshold. Depression is still -12. Always resist arrest, so always being beaten. I'm just waiting for PTSD pops up for further misery.
I have a suggestion that mod Grimreality may be in charge, as a mod modifying moodlets.

You need to arrest people with your highest Social colonist.

I also have a colonist with -12 Depressive despite treatment, and am also using Grim Reality if you are looking to narrow down the cause. Hope that helps.