When dealing with parent / children entities, the UnitOfWork does not always hydrate all data correctly.
This example generates Group1 and its child Group2. Then Clears the Entity Manager, loads Group2 (so it is in the EM), loads Group1 and then the children of Group1 (Group2 is the child of Group1).
However the children of Group1 cannot be loaded, because $group4->children is not there:
When calling Debug::dump($group4), I get this: