On using User Search Rest API to search for users ( /rest/api/2/user/search?query= ), it does not return results in the same order. 

Example- If we want to search for users whose name start with "T", it will return all the users but every time the search is run, the order would be different. 

This creates problem if we want to look for one user at a time and the result will return a different user every time the query is run making results unreliable.