I think there may be more than one bug being described in the comments.

HHH-10562 - ManagedEntity linked list broken when lazy loading enabled: previous and next are null New covers a case where the EntityEntryContext can be corrupted when EntityEntryContext#removeEntityEntry(Object entity) is called for an entity that is not in the EntityEntryContext. I believe Jörg Waßmer is running into this issue.