Hello!
So I'm in a server and we have show me your skin and both the Better End and Better Nether mods,

Within those mods,
BetterNether armour works, and in BetterEnd all the armour except for Crystallite works

Crystallite shows up no matter what. I'm not sure if this has to do with the fact it always is giving the player alternate effects like haste, speed and extra health? But we wanted to submit a ticket to hopefully see a fix?

Cheers. Images below.
Wearing Crystallite

Wearing any other armour (diamond, etc)

The armor might be using a custom renderer without going through Fabric Rendering API properly. I cannot control the transparency for the armor of mods that do this. A fix would have to come from Better End.