Checking T198233: Allow musical notation to be expressed in Wikidata, with rendering and maybe playback revealed that the contrabass MIDI instrument is unavailable through the MediaWiki configuration of TiMidity++ (in @Jc86035's case, replaced by cello). Replacing it, there is no audio output.

This is fixed by changing the "soundfont" being used by TiMidity++ to a different soundfont (not the default freepats) by installing fluid-soundfont-gm & fluid-soundfont-gs in Puppet and updating /etc/timidity/timidity.cfg to point to /usr/share/sounds/sf2/FluidR3_GM.sf2. (where?)

Another solution would be with the migration to fluidsynth, with a checklist provided by T184598: Enable Score MP3 support for Wikimedia wikis.