Current bug:
Shield patterns stop displaying entirely once a new shield geometry replaces the vanilla one within a resource pack, even if both geometries are identical.

The way it should work:
Shield Patterns should still be displayed when a resource pack changes the geometry of the shield.

Bug demonstration:
A Resource Pack (Shield_patterns_bug.mcpack) has been attached to this issue to demonstrate the error along with a couple videos. It would only need to be imported and applied in-game. The Resource pack only contains a geometry file that replaces the shield model with one that is exactly identical to the one currently in the base game. The shape of the model does not matter, as soon as the game loads a geometry model for the shield from a Resource Pack, Shield Patterns will stop working.