When you wear a classic skin with a cape attached, it won't show the elytra making it look weird. I think it does this because the elytra changes it's texture when you wear a cape and the skin I use has a cape attached that has no texture for the elytra making it invisible. The skin used that caused this was the ender dragon skin from this skin pack (https://www.minecraft.net/en-us/pdp?id=8e78a44d-0c1f-4ce2-826b-8bbc555012de#)