Hope the return journey is smoother. Enjoy the event.
Thanks! I forgot to mention the positives. We saw the start of rage Zermatt Gronergat marathon from the train. The start was way downhill at St Niklas. People lined up for the bus at Geneva airport were very helpful, the lady at Avis gave us our car despite our lateness and she was under pressure by others...
And the local services are indeed superbe :).
Read something on a Swiss news website about rail tracks buckling in the heat at La Plaine (just outside Geneva on the line that goes to Grenoble, and normally to Paris), which might explain this. There were also weekend works on the Lausanne-Geneva line when I was there (and hence a lot of long-distance trains weren't going beyond Lausanne), so I guess that's still the case.
The heat issue makes a bit of sense. There was a photo in the station at Chambery showing some tracks under landslide, which may have been the result of thunderstorms. My French was not god enough to work out whether that was the particular problem for us. It all worked in the end and the buses were a very good alternative. After the experience, I would use them again.