Minecraft Version: 1.21.1 Fabric
Mod Version: 1.6.2-1.21.1
Using an enderite elytra armor to fly, the unbreaking enchantment on it seems to have no effect. The durability of the item drops fast like a regular elytra with no enchantment.

To reproduce:

1. Enchant enderite elytra (with armor) and a regular elytra unbreaking 3.
2. Use them to fly around, and check the speed of durability dropping of each item.

Expected result:
The speed of durability dropping should be nearly the same, only have slight difference.

Test result:
Enderite elytra (with armor) loses durability faster than the normal elytra. (Flying 1 minute, the normal elytra drops 15 durability, while the enderite one drops more than 60.)

I don't know whether this is a way to balance this equipment, but I see no point for such action, as many players love the idea to combine the armor with the elytra.

Ehem, soooooo let's make this short:

Vanilla Bug

https://bugs.mojang.com/browse/MC-278983?page=com.googlecode.jira-suite-utilities:transitions-summary-tabpanel
This appears to be a vanilla bug. The issue isn’t that something doesn’t work, but rather that the Unbreaking enchantment behaves differently on certain items compared to others (specifically, armor vs. the Elytra).

You can reproduce this by giving yourself a diamond chestplate with the glider component: /give @s minecraft:diamond_chestplate[minecraft:glider={},enchantments={levels:{unbreaking:3}}]
The enchantment still works but is less effective than on an Elytra. Here are the damage numbers observed after 20 seconds of flight:

• Without enchantment: 20-21
• Elytra (Unbreaking 3): 6
• Enderite Separated Elytra (Unbreaking 3): 5
• Enderite Elytra Chestplate (Unbreaking 3): 18
• Diamond Chestplate (Unbreaking 3): 16

Cause of the Issue

The problem lies in how Mojang handles item tags. There’s a tag called #minecraft:enchantable/armor, which determines what enchantments can be applied to armor items.

The Unbreaking enchantment uses this same tag, but it behaves differently depending on the item type. Since both the Diamond Chestplate and the Enderite Elytra Chestplate need to be enchantable with armor enchantments, they must be included in this tag. However, this inclusion causes the Unbreaking enchantment to function less effectively on these items compared to the Elytra.

Solution?

1. Remove the Enderite Elytra Chestplate from the Armor Tag

By removing the Enderite Elytra Chestplate from the #minecraft:enchantable/armor tag, you can achieve the Elytra Unbreaking behavior. However, this would also prevent the armor from receiving armor enchantments. As a workaround, you would need to enchant the chestplate before crafting it.

To implement this change, modify the file data/minecraft/tags/item/chest_armor.json in the enderitemod.jar as follows:

{
  "replace": false,
  "values": [
    "enderitemod:enderite_chestplate",
    "enderitemod:enderite_elytra"           // REMOVE THIS LINE
  ]
}

Note: This change will break armor enchantments for any already crafted Enderite Elytra Chestplate.

2. Adjust the Durability via Config

Alternatively, you could modify the armor durability settings in the configuration to balance the issue without removing the tag.

Conclusion

So technically it is not a bug, but intended behavior of the Unbreaking enchantment for armor items.
(See comment in bug tracker)

If you have any more question feel free to ask.

@Pitti11
Well, thank you for your work on this problem. I don't know this is a vanilla bug, and sorry for wasting you too much time. I will try the method you provide to work around.

Thanks again for your help.

Quick testing confirms the Enderite Elytra takes too much damage with unbreaking. Further, the seperated Enderite elytra does behave as expected, but both have the same vanilla components. So it may be a result of the Enderite Elytra being both a chestplate and an elytra.

We will look into it.

Quick testing confirms the Enderite Elytra takes too much damage with unbreaking. Further, the seperated Enderite elytra does behave as expected, but both have the same vanilla components. So it may be a result of the Enderite Elytra being both a chestplate and an elytra.

We will look into it.

Thank you for your attention. I changed the title and the comment to make the contents more clear.