Hey, I found that your all your RPG Series Mods for classes show as a missing texture error on that mod when using them as cosmetics for some reason. Not really sure what could be causing the issue.

https://modrinth.com/mod/cosmetic-armor

This is likely an issue between Cosmetic Armor and AzureLib Armor (the library which implements custom 3D armor models).
There is nothing I can do. Sorry.