It is possible that your document has corrupt field codes in it. We have a FAQ on our web site that gives the steps to remove all of the field codes and clean up the document. You should first make a backup of your Word document and then follow the steps in the FAQ at:
If that does not help then I would contact Technical Support
1-800-336-4474 or
https://support.clarivate.com/Endnote/s/technicalsupport?language=en_US