Signals Notebook: When we create a New User, "Alias Already Exist" message appears but there is not the same alias in the Signals Notebook

When we create a New User A, "Alias Already Exist" message appears or "The email address is already Exist" message appears when we update created User A without Alias field filled but when we download the list of current users there is no the same alias in the downloaded .csv file.

Solution: Current List of Users, that is being downloaded from Users page, contains the list of active Users, there are no deleted Users. All deleted Users should be reviewed as well to find a User with the same alias.