Error with attributes

Hello,

I have an error with my custom mythicmobs items. In game the attributes are displayed under the item's lore but are not applied.

Here is an example :
armor:
Id: 307
Display: '&armor'
Lore:
- '&6test armor'
Attributes:
Chest:
Armor: 20
KnockbackResistance: 60
Enchants:
PROTECTION_FIRE: 5

Then in game, in my inventory I can read :
When on body :
+20 armor
+60 knockback resistance

however I have only 3 plate pieces above my health bar instead of...

Error with attributes