The Cesium plugin has become too hard to maintain. For the moment I've switched back to using Google Maps, which unfortunately doesn't make the different track speed segments very obvious. On the other hand, there is a map, and the track is at least pinned to the ground, which we've also been having problems with recently. If you want to analyse the track in more detail, do as suggested above, click the (KML) link to download the file and open it with Google Earth. This gives a much richer experience.
