If an enchantment foil is applied to quads that are facing in opposite directions but occupy the same space, the foil will z-fight with itself. This is most easily noticeable on item models that are both animated and enchanted.
Attached is a resource pack that replaces the enchanted book texture with one that demonstrates the bug. The model edge between the two pixel lines will experience z-fighting. A screenshot of this edge is also attached.
Does MC-167526 describe your issue?