The bug

When you have an item that is enchanted, it has an aqua-color and is in italic. But these JSON text effects disappear when it's in an item frame (and has a custom name which makes the name visible inside an item frame in the first place).

This can be replicated by using the following command:

/give @p stick{Enchantments:[{}],display:{Name:"{\"text\":\"i'm a stick\"}"}}

 
To fix this, make the item frame take in account whether an item is enchanted for providing the display of the name inside the item frame (since an item frame displays something different as inside the inventory and doesn't always display the name of an item, this should be possible).