Pdf double endnote issue

This is a test docbook file that shows a good ePub output but double (and weird) endnote issue with pdf output:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-model href="http://docbook.org/xml/5.1/rng/docbook.rng" schematypens="http://relaxng.org/ns/structure/1.0"?>
<?xml-model href="http://docbook.org/xml/5.1/sch/docbook.sch" type="application/xml" schematypens="http://purl.oclc.org/dsdl/schematron"?>
<article xmlns="http://docbook.org/ns/docbook"
    xmlns:xlink="http://www.w3.org/1999/xlink" version="5.1">
    <info>
        <title>This is a test Docbook</title>
    </info>
    <sect1>
        <title>First Section</title>
        <para>This links to first endnote[<xref linkend="Ref1"/>]</para>
        <para>This links to second endnote[<xref linkend="Ref2"/>]</para>
        <sect2>
            <title>Endnotes</title>
            <para>
                <orderedlist>
                    <listitem>
                        <para xml:id="Ref1"> www.google.com </para>
                    </listitem>
                    <listitem>
                        <para xml:id="Ref2">Doe, J. "This is a Docbook". Journal of everything XML. 2021:1(1):1-2.</para>
                    </listitem>
                </orderedlist>
            </para>
        </sect2>
    </sect1>
</article>