Notes missing from staff 5 on musicxml import

I'm transcribing a piece for organ using 5 staves, one for each voice (I know this is not how organ music is usually written, but this isn't meant for human performance anyway).
I tried exporting the piece to .musicxml and importing it back into Musescore, and every measure in the fifth staff is filled by an invisible whole measure rest. I attached to this post both the Musescore file, and the file I got when exporting to .musicxml. Both of them were generate with Musescore 4.0.1-230121751 on Windows 10, however the issue on import also happen with Musescore 3.6.2.548021803.

The .musicxml file itself seems to have been generated correctly (for what I can understand at least). For example on measure 28 in the fifth staff there is a G whole note, and in the .musicxml file you can see on line 9824:

      <note>
        <pitch>
          <step>G</step>
          <octave>2</octave>
          </pitch>
        <duration>32</duration>
        <voice>17</voice>
        <type>whole</type>
        <staff>5</staff>
        </note>