SharePoint Online Custom Form Breaks After Editing with SharePoint Designer

Question

I am encountering an issue with SharePoint Online when editing a custom list/library form using SharePoint Designer. Here are the steps to reproduce the issue:

1. Open an editform.aspx file in SharePoint Designer 2013 in Advanced Mode.
2. Without making any manual changes to the file, simply save it.
3. After saving, the form breaks and displays the following error: Unknown server tag 'WebPartPages:DataFormWebPart'. Correlation ID: XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

This issue occurs consistently across multiple lists/libraries, even when no actual changes are made to the form's code. It appears that SharePoint Designer modifies the markup upon saving, which is causing the problem.

Details:

• Environment: SharePoint Online (Office 365).
• Tools Used: SharePoint Designer 2013.
• Impact: The custom forms for my SharePoint lists/libraries are unusable after saving them.
• Actions Taken:
  • Attempted to revert to previous versions (partially successful).

     - Verified that SharePoint Designer alters the code without user intervention.
    

Please investigate and provide guidance on how to resolve this issue or confirm if it is a known bug in SharePoint Online/SharePoint Designer.

Answer 1

I did a test in my SharePoint Designer 2013, saving edit form works well in it.

Whether your account with MFA enabled?

Try use another account to save edit form to SharePoint Designer 2013, check whether the issue exists.

You could follow below tips to troubleshoot the issue.

1.Clear cache. In the local computer, remove all files found in each of the following folders. Then open SharePoint Designer 2013 and enter the account again to see if it works.

• %APPDATA%\Microsoft\Web Server Extensions\Cache
• %APPDATA%\Microsoft\SharePoint Designer\ProxyAssemblyCache
• %USERPROFILE%\AppData\Local\Microsoft\WebsiteCache

2.Verify that SharePoint Designer 2013 is updated with SharePoint Designer Service Pack 1 and the August 2, 2016, Update for SharePoint Designer 2013.

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