I have backend implementation that adds property under preference node. Example /home/users/S/aiowerlakjf_lkjwer/preference

I am using service user to update user preference. All the users' preference are updating as expected, however there is one user which is replicated, preference of this user is not updating. The only difference between this user and rest of the users is, it is replicated. 

I am not sure why would this even be an issue. 

I would appreciate if you can share your experience related to updating users in AEM and if you have encountered similar issues.