Item models can no longer access textures in /minecraft/textures/entity folder. i have item models (spawn eggs, armor, fish, signs) that use textures in /minecraft/textures/entity, they are now black/purple, i can fix by copying the textures to /minecraft/textures/item, and updating the models but that is a big waste to have mutiple copys of a texture.
Please check out MC-256668 for instructions on how to fix your pack 🙂