For this particular instance, we resolved the issue by doing a Restore Defaults on the portlet for the user. Clicking Show All on the portlet displayed other users, but the one user was not displaying for the user when filtering specifically for that user.
Steps to resolve:
1. For the user with the issue, go to the Resource Workloads portlet and click Options->Configure
2. Go to General tab and click Restore Defaults
Then the resource was able to see the user in the portlet.