Hate to be that guy but I seem to be having an issue with the EMS versions of both the head and torso. Perhaps it's some kind of clash with another mod, but hard to say, I've not run into this before. Screenshot provided.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2755725194

2 of the 3 torsos are just textureless and black for me

same for me

You're not the only one. This and the actual MEC enemy were the very first mods I've downloaded for XCOM 2 WoTC, and the Colorable EMS Head, Body 4 and Body 5 doesn't have any textures. (Body 5 is only missing it's torso textues, the giant ammor rack on it's back is that same.)
Now, for me, this isn't anyhting that ultimately would ruin the experience. The MEC itself works perfectly, and I wouldn't be suprised if those texture-less pieces are just accidental leftovers.

Black textureless for me too