User does not appear on LOV for Reassigning BPM Approval

Summary:

User is missing from the Name LOV in the Reassign dialog box.

Content:

I have an issue in BPM when reassigning an approval notification, in this case an invoice approval. I am trying to reassign this to another user, but their name does not appear in the search box, as shown here:

We have two people with the same name. In the example above, only one of the two users come up and not the correct one. If we click More , we can find the correct person using advanced search.

Any thoughts on why this may be and how to resolve?