Wearing cape textures as your skin makes your body partially invisible on multiplayer servers.

If you wear any cape texture (64x32 pixels .png file) as your skin, your body will be partially invisible for other players in multiplayer servers and for yourself (sometimes).

I believe the skin becomes invisible to the players that have the cape texture file on .minecraft files (the skin of the player is rendered with the same parameters of .png cape texture file), so the glitch is more noticeable with capes that have more users, such Migrator Cape and 15th Anniversary Cape.

The screenshot attached was taken on Hypixel, while wearing the 15th Anniv. Cape with cape and 2nd layer of the skin disabled.

I don't know if the glitch happens on realms too, since I don't subscribe it.