The problem is when Author has two or more publications in a year, then the first line of the BibTex download is not unique for these articles, they all begin with:
@article{Author_2018, title={blah blah …
I suggest this should be amended to:
@article{Author_2018_xxx_9_3_235, title={blah blah …
where xxx is the journal initials, followed by volume, issue and page number
I managed to do this by by adding three lines in
plugins/generic/citationStyleLanguage/citation-styles/bibtex.csl
<macro name=“citeKey”>
<group delimiter="_">
<text macro=“author-short” text-case=“lowercase”/>
<text macro=“issued-year”/>
<text variable=“volume” prefix=“ph.nv_”/>
<text macro=“number”/>
<text macro=“pages”/>
</group>
</macro>
but hard coding the journals initials as ph.nv which would need to be replaced with proper coding.
It would be great if this, or any other scheme for uniqueness, could be implemented permanently,