capes and elytras not appear in custom skins

so, when i try to use a custom skin (that ones that you upload externally) both the cape and the elytra(both with cape skin and without it) not appear,they are invisble

Img 1 - only cape, not elytra
Img 2 - proof that i equiped the cape
img 3 - flying with the ¨elytra¨