Refers to CleanroomMC/ModularUI#157.
ModularUI adds a resource type which is gui theme json files. This mod only checks for vanilla resource types here and then just assumes its an item model here.
Why are you not just checking startsWith("models/item")?

This an extension of #1952 and i just saw that it was fixed in f8a47fe, but again its a very primitve fix and should be fixed with a startsWith("models/item") check.