我也遇到这个问题，百度了半天没答案，发邮件去问了endnote的客服，这是回复：
As a test please open a blank new Word document and randomly insert a few citations to check the functionality.
If the new document works fine, then the issue could be due to damaged field codes in the particular document. Field codes are the hidden codes that hold the reference information.
Please try to recover your document by cleaning the field codes with the steps given below:
On Windows:
Make a backup of your document.
In Word 2010/2013/2016 with Endnote X4 or later, go to the EndNote tab and choose the "Convert Citations and Bibliography > Convert to Unformatted Citations" command.
This will remove the reference list and revert the citations to a temporary format.
Press [Ctrl]+A on the keyboard to highlight everything.
Press [Ctrl]+6 (above the "T" and "Y" key) to remove any additional hidden field codes.
Go through the document and remove/erase the extra citations manually. Only keep the unformatted citations which look like {Author, Year #123}
Press [Ctrl]+C to copy the highlighted text.
Open a new document and press [Ctrl]+V to paste.
On EndNote (version) tab, click on "Update Citations and Bibliography"