SharePoint Designer 2013 - a new "SharePoint 2013 Workflow" won't open

Ran into an issue today where SPD13 would not open up a SP13 Workflow.

The "SharePoint 2013 Workflow" Platform Type was there and it would attempt to open with a "Generating Local Cache" Pop-up box, but would just blank out after that with no empty workflow opened.

Originally, I thought it must be the workstation, but it worked against another SP13 farm in the same network.

After troubleshooting, it took a clearing of the config cache on the SP13 WFEs on that farm to resolve the issue.