A workflow step appears to be assigned to a resource, but the resource requests are not listed in the workflow reminders page
This can happen when the workgroup has been removed from the resource request. When a resource request is created, the workgroup is assigned automatically, however users can remove the workgroup before saving the request.
Workaround
Edit the resource requests to select a workgroup.
To prevent users from saving a resource request without a workgroup, consider making the workgroup field a required field for resource requests. The field name is "ManagerWorkgoup" in Metadata.