Hi @petersonal ,
For troubleshooting the issue, you could check things below:
1.Clear the SharePoint Designer cache to check if it can work. For more information, please see "How to Clear Your SharePoint Designer 2010/2013 Cache" article.
2.Run SharePoint 2013 products configuration wizard to repair the SharePoint environment.
3.Run IIS Reset to check if it can work.
Thanks,
Echo Du
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