Merged GPX file fails validation

[KronosTheLate]

Merging two files that are valid produces a resulting file that has the following errors:

S4s-elt-character: Non-whitespace Characters Are Not Allowed In Schema Elements Other Than 'xs:appinfo' And 'xs:documentation'. Saw 'Document Moved'., Line '1', Column '28'.
The Markup In The Document Following The Root Element Must Be Well-formed., Line '2', Column '2'.
The Markup In The Document Following The Root Element Must Be Well-formed.

I used this page for validation, as reccomended here.

File 1 contents

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="Colota" xmlns="http://www.topografix.com/GPX/1/1">
  <metadata>
    <name>Colota Location Export</name>
    <time>2026-05-20T22:04:53.000Z</time>
  </metadata>
  <trk>
    <name>Colota Track Export</name>
    <trkseg>
      <trkpt lat="62.424161" lon="6.274748">
        <ele>78</ele>
        <time>2026-05-20T10:14:42.000Z</time>
        <extensions>
          <accuracy>19.296001434326172</accuracy>
          <speed>0</speed>
          <battery>35</battery>
        </extensions>
      </trkpt>
      <trkpt lat="62.423844" lon="6.275863">
        <ele>87</ele>
        <time>2026-05-20T20:06:47.000Z</time>
        <extensions>
          <accuracy>68.60800170898438</accuracy>
          <speed>0.6600000262260437</speed>
          <battery>12</battery>
        </extensions>
      </trkpt>
    </trkseg>
  </trk>
</gpx>

File 2 contents

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="Colota" xmlns="http://www.topografix.com/GPX/1/1">
  <metadata>
    <name>Colota Location Export</name>
    <time>2026-05-20T12:27:43.000Z</time>
  </metadata>
  <trk>
    <name>Colota Track Export</name>
    <trkseg>
      <trkpt lat="62.424161" lon="6.274748">
        <ele>78</ele>
        <time>2026-05-20T10:14:42.000Z</time>
        <extensions>
          <accuracy>19.296001434326172</accuracy>
          <speed>0</speed>
          <battery>35</battery>
        </extensions>
      </trkpt>
      <trkpt lat="62.424104" lon="6.275333">
        <ele>63</ele>
        <time>2026-05-20T10:17:32.000Z</time>
        <extensions>
          <accuracy>254.0640106201172</accuracy>
          <speed>0</speed>
          <battery>34</battery>
        </extensions>
      </trkpt>
    </trkseg>
  </trk>
</gpx>

Merged file contents

<?xml version='1.0' encoding='utf-8'?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd" creator="https://github.com/sgraaf/gpx">
  <trk>
    <name>Colota Track Export</name>
    <trkseg>
      <trkpt lat="62.424161" lon="6.274748">
        <ele>78</ele>
        <time>2026-05-20T10:14:42Z</time>
        <extensions>
          <accuracy>19.296001434326172</accuracy>
          <speed>0</speed>
          <battery>35</battery>
        </extensions>
      </trkpt>
      <trkpt lat="62.423844" lon="6.275863">
        <ele>87</ele>
        <time>2026-05-20T20:06:47Z</time>
        <extensions>
          <accuracy>68.60800170898438</accuracy>
          <speed>0.6600000262260437</speed>
          <battery>12</battery>
        </extensions>
      </trkpt>
    </trkseg>
  </trk>
  <trk>
    <name>Colota Track Export</name>
    <trkseg>
      <trkpt lat="62.424161" lon="6.274748">
        <ele>78</ele>
        <time>2026-05-20T10:14:42Z</time>
        <extensions>
          <accuracy>19.296001434326172</accuracy>
          <speed>0</speed>
          <battery>35</battery>
        </extensions>
      </trkpt>
      <trkpt lat="62.424104" lon="6.275333">
        <ele>63</ele>
        <time>2026-05-20T10:17:32Z</time>
        <extensions>
          <accuracy>254.0640106201172</accuracy>
          <speed>0</speed>
          <battery>34</battery>
        </extensions>
      </trkpt>
    </trkseg>
  </trk>
</gpx>

[KronosTheLate]

Note that a file created with the gpx python package has exactly the same issues, so I also raised this issue over there