After #29 the settings are apparently not readable anymore, even though nothing obvious changed, it's still the same settings.ini path, same contents etc. Anyways, this will fix it:
- find the QGIS settings path, e.g. on Linx
QGIS_SETTINGS_PATH=~/.local/share/QGIS/QGIS3/
- find the valhalla settings.ini which should be
$QGIS_SETTINGS_PATH/profiles/default/valhalla/settings.ini (or another profile if you set one)
- remove that file and restart QGIS