I did a search but could not find anything recent relating to duplicate bibliography entries.
I upgraded from x8 to x9 recently on my iMac High Sierra.
I have written another document recently where this issue never occurred it is only the document I started recently that I find the issue happening.
Word choose References - Insert Footnote,
EndNote x9 select a reference and Insert citation,
Word refreshes including the footnote text from x9,
Word/x9 duplicated the existing bibliography entries and includes the new one.
Has anyone else seen this and know what the solution to the bug is, please?