Equip sound in Equippable component cannot be set to a sound event from a resource pack

When setting a custom equip sound for an item, the field only accepts built-in vanilla sound events. Sound events added via Resource Pack are not accepted, despite armor materials themselves from a resource pack working just fine.

To reproduce this bug, create a resource pack that adds a custom sound event using a sounds.json. You will know you have done it correctly when /playsound's autofill has your custom soundEvent as an option. Now try to spawn armor that makes this sound event when equipped, such as:
/give @p minecraft:diamond_boots[item_model=frogspawn,minecraft:equippable=\{slot:feet,model:diamond,equip_sound:"custom.shriek"}]
Replace 'custom.shriek' here with your sound event. It will not work, though putting in a vanilla sound event such as block.anvil.destroy will.