Verum I think it is related to this as I've stated on Discord or on GitHub
ARMORS ARE LEATHER 1.21
Hey everyone, I don't know all of you but surely you know of me I wanted just to say you, when you'e using 1.21 instance of Minecraft and have custom armors AND you have a problems with it, please follow this tutorial
Open config.yml
in your ItemsAdder folder in plugins folder
Search for generate-custom-armors-textures:
Enable vanilla
and DISABLE vanilla_1_17
/iareload
and /iazip
Enjoy your armor (shaderpacks are still not supported)
PS: when you keep vanilla_1_17 enabled it autodisable the vanilla, when you're new into IA and it's your first install, probably you have not the vanilla_1_17)