Issues with workbench moderation
I faced the same issue where 'Needs Review' tab appeared empty after the workbench moderation state for conten type is set to 'Needs Review' or 'Draft'by the creator.
I applied a patch from drupal.org and it worked. Please find the below patch and apply it in your Workbench Moderation module.

https://www.drupal.org/files/node_revision-1363990-2.patch

Let me know if you still face an issue.