One of my customers has reported seeing the following message when working in documents created from templates that I provided:
This file has Custom XML elements that are no longer supported in Word. Saving the file will remove these elements permanently.
I understand that this message relates to Custom XML Markup (https://learn.microsoft.com/en-us/office/troubleshoot/word/custom-xml-elements-not-supported). I can confirm that there is no Custom XML Markup in the document.
Any idea what could be causing this error to display?