Enchanted books lose enchantments on upgrading from 1.12.2 to 1.13-pre3.

To reproduce: -

• create a world in 1.12.2
• put an enchanted book in a chest (single or double)
  
  
• open world in 1.13-pre3
• look at enchanted book
  
  

The books seem to have NBT data but don't display any enchants and don't work in an anvil: -