Ok, I was wondering if my Syl skin had the same glitch with the animations, and It has. It's just a fraction of a second so you won't notice if you don't pay attention, but is there. The issue seems to happen when the animation rotation changes from one animation into the same, for example Pistol1  ->  Pistol2 -> Pistol1 won't make the glitch appear, but pistol1  -> pistol1  -> pistol1 make the glitch happen on every inbetween


Ok, so I have been testing the animation glitch so here is my experience with it:
@Kva3imoda say it right, if a player models has no wardrobe base or has wardrobe set to false,  the animation glitch is going to happen.
I tried this with my Syl model, but using her texture as a wardrobe base made the game glitch the model as if it wouldn't load, just like @Vkoslak . The issue was that my texture had alpha transparency, after deleting the alpha channel on the texture it worked, and my model load properly and without the glitch.
But then I got the last part, since now my model has wardrobe ON and working, equiped items show on her... but to fix this, I only added a RACE to her. I didn't have to edit any items or even the wardrobe file, just adding the RACE to player unit made that the armor stay hidden.
So the conclusion to make a non-wardobable player:
<BOOL>WARDROBE:1
<STRING>WARDROBE_BASE:[PNG Texture without alpha, size doesn't matter]
<STRING>RACE:[Anything works excepts HUMAN]
There is one thing I haven't tested if is needed or not, but my model has its material named NPC_Syl/Chest like a PC model, even if it doesn't has submeshes.