If you created a custom CIT for leather armor it might not work.
In order to fix this you have to make sure to add the weight attribute to your custom CIT, this makes Optifine prioritize your CIT and it will load it correctly.
Example:
type=armor
items=leather_helmet leather_chestplate leather_leggings leather_boots
texture.leather_layer_1=my_layer_1
texture.leather_layer_2=my_layer_2
nbt.display.Name=ipattern:My Custom Armor
weight=99999