Hi @Fortner, Thomas ,
Apart from trying the advice given by sharatha, to narrow down your issue, let’s confirm the followings:
- Does this issue occur on other lists of the same site collection?
- You can create a new custom list in your site collection via UI and test if forms can be created for it in SharePoint Designer.
- Can you create a new item normally in your problem list? If you are unable to create an item in the list, please check whether there are broken Lookup column or Calculated columns in your list. Go to delete them and recreate in your list. There is a similar case for you to refer to: https://drewmadelung.com/sharepoint-designer-error-could-not-save-the-list-changes-to-the-server/
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- How did you clear the cache? Please refer to this article to clear SharePoint Designer 2013 cache: How to Clear Your SharePoint Designer 2010/2013 Cache
- If everything I mentioned above doesn’t work for you, please check whether there are some related error messages in ULS logs.
I hope this information has been useful, please let me know if you still need assistance.
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