1.18.1 Fabric with sodium and iris shader, if that's relevant. Using latest version of mcda.
Using cosmetic armour and a bunch of other mods too.

When equipped (normal or cosmetic slot) all pieces but the arctic fox leggings show their model. The pants part of the character render as transparent.

This is actually just the way that the texture artist (SeaOfPixels) did the texture. There is no rendering issue, but I appreciate you bring it to our attention :)