Cadence data not read from FIT or written to GPX

[routeconverter]

Thank you, that file showed that osmand is using custom extensions:

<extensions>
  <osmand:provider>gps</osmand:provider>
  <gpxtpx:TrackPointExtension>
    <gpxtpx:atemp>19.32</gpxtpx:atemp>
    <gpxtpx:cad>15</gpxtpx:cad>
    <gpxtpx:hr>99</gpxtpx:hr>
  </gpxtpx:TrackPointExtension>
  <osmand:heading>68.0</osmand:heading>
  <osmand:speed>5.4</osmand:speed>
</extensions>

RouteConverter currently is only able to read speed from the GPX file (I don't know why ;-)) because it doesn't know the other extensions yet.