Arcade can't find existing user

We got a user which has 2 scores, both of them "best score of all times".
When looking for his name via the Member Manage option in the arcade, the user is found.

But when I click "edit scores" I get the message "No scores set by this user".
Even when I try to lookup his scores with the Score Tools option, no scores of him are found.

How can this happen, and how can I fix this?

Next to that I have a game which 'best score of all time" got pruned, but I didn't do that. How can this happen?