With texture packs in 1.15, any items with the predicate "Custom_model_data" applied within their .json model files show up as blank textures, even if the {CustomModelData} NBT tag has not been added to the NBT of an item.

All items tested with worked in version 1.14.4.

The textures themselves work in 1.15 and can be applied by changing the file path designated in the .json file, so I believe this may be an issue with CustomModelData in 1.15.

I've attached a copy of my resource pack below if it's any help.