About Options.AppendType: false
The issue is about Options.AppendType: false. I create an item and import the item using command /mythicmobs item export. After that, Options.AppendType: false is added in the item.yml. When the item is dropped from the mobs, there is still a NBT: MYTHIC_ITEM_VERSION:1. The item cannot be stacked with the item that I created before.
The issue does not happen in mythicmobs.5.0.2. It only happens in mythicmobs 5.0.4. Please fix this bug in the future version.
This is the NBT of the item that I create.
This is the NBT of the item that is created by mythicmobs.5.0.4.