When Wavey Capes (Forge) is installed, the cape does not disappear when elytra is equipped in the Curios slot added by Curious Elytra. It also doesn't disappear if wearing a customizable elytra from the mod of the same name (this probably also occurs on the Fabric version too).

Expected behaviour, of course, is that the cape should disappear when any elytra is equipped in any slot.
To reproduce, just equip a customizable elytra, or equip any elytra in the Curios slot.

Supposedly this is because Wavey Capes is currently hardcoded for the vanilla elytra.
Issues raised on github for the other mods:
Hidoni/CustomizableElytra#15
illusivesoulworks/elytraslot#32

System Info:
Minecraft Version: 1.16.5
Forge Version: 36.2.9
Wavey Capes Version: 1.0.4 (forge)
Customizable Elytra Version: 1.5.7 (forge)
Caelus Version: 2.1.3.1
Curios Version: 4.0.5.3
Curious Elytra Version: 4.0.2.3
Java Version: 1.8.0_242 64bit
CPU: 16x AMD Ryzen 9 5900HX with Radeon Graphics
GPU: NVIDIA GeForce RTX 3070 Laptop GPU/PCIe/SSE2

I'll have to look into how to correctly get slots added by other mods(kinda problematic since it's Fabric and Forge). Probably also needs a list of other mods elytra items.