To me that sounds like a permissions issue. Check the "All Users" permissions if you are experiencing issues where users can only see the work that they have published. Also remember permissions at the workbook level will over ride project permissions, so you may need to check on a workbook level as well.
.....as it turns out, we rebooted the Tableau Server and everything went back to normal..
Chris, thanks for letting us know your fix and marking it as Answered