Missing skin for MPS legs (Citizen Joe + Default)

[Murkuin]

Sorry if this isn't the right place post this, wasn't entirely sure who to ask.

So I'm using the 1.12.2 pack on a server, and when I tried to change my MPS leg armour to Citizen Joe they simply turn invisible instead. This also happens with the default skin, but not with either of the 3D skins, nor with the helmet, chestpiece or boots. Has anyone else had this issue / solved it?

Any help would be greatly appreciated, I'll provide a video if necessary