The bug

In MC 1.14, the translucent elements will see through other elements in the same model based on their position in the layer, but after MC 1.15, translucent elements are no longer affected by layers to see through the elements.
The "layer" I'm talking about is the element's orderh3.The bug
In MC 1.14.4, the translucent elements will see through other elements in the same model based on their position in the layer, but in MC 1.15, translucent elements are no longer affected by layers to see through the elements.
The "layer" I'm talking about is the element's order in the JSON file.

How to reproduce

1. Download the resource pack and load it into the game
2. Get a diamond sword with CustomModelData NBT tag

   /give @s minecraft:diamond_sword{CustomModelData:1}
   /give @s minecraft:diamond_sword{CustomModelData:2}
   /give @s minecraft:diamond_sword{CustomModelData:3}
   /give @s minecraft:diamond_sword{CustomModelData:4}
   

3. Switch to the first-person view and hold the item in your hand
4. See the different on all four items

• MC 1.14.4 and before
  → Each item have a different look

• MC 1.15 and After
  → All four items look same