@sns
Try to install Service Pack 1 for SharePoint Designer 2013. Then clear SharePoint Designer 2013 Cache.
If this issue persists, you could try to reinstall SharePoint Designer 2013. Maybe this issue is related to order of installation of SharePoint Designer 2013 and Visio. So try to uninstall both, then install Visio first, after that install SharePoint Designer 2013.
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