Steps to Reproduce:
1. Change a dog data "Owner" with an entity UUID so it will follow the entity (a zombie for example)
2. Save a custom structure as nbt file using the structure block, with both the dog and the zombie in it (so the entity will generate with the structure)
3. Use the Structure Block to load the structure in the world (so a new zombie and a new dog will spawn)

Observed Results:
The new dog will have as owner the firt zombie saved in the structure, the UUID in the new dog's Owner data dosen't match the new zombie's UUID 

Expected Results:

The new dog should be owned by the new zombie when generated, 

1 picture: saved structure, same UUID for Zombie and Dog's owner

2 picture: loaded structure, different UUID, Dog's owner is the same as the first picture