I just looked at the reputation history of this user. It does say that the user is not registered. But I still don't understand how this pattern of reputation changes can happen. Please, take a look at the history of changes in the screen capture below:
How does a user get only 1 rep for an upvote of a question? Why would upvotes after that stop adding to their rep? Is this a bug? Or was this caused by some status change of the user?