Using Lapito's Galacticraft modpack 8.8.6.8 on minecraft 1.12.2
When I put on the armor, the 3D model appears broken

This is without any resource packs or shaders. However when I do put shaders on, it looks even worse.

This is only happening with the MPS models and the helmet of the Armor 2 model (when changing visuals in the tinkers table).

EDIT: Found out it is a shader issue, if shaders were on, even if I turn them off the 3D textures bug out, and I have to restart the game. So problem solved I guess, just can't use shaders

Unfortunately I have not been able to get the development environment working for 1.12.2 in several years and it has been unsupported by Forge for about 5 years now. The best I can do currently is advise you to try disabling other mods in the pack until the issue goes away.