This is a bit of an inevitable byproduct of the way cycle.travel works I’m afraid. If something changes in the underlying map data after when you first created your route, or if cycle.travel’s weightings have been adjusted, then anything that requires the route to be recalculated (which currently includes the Garmin Connect export and the elevation display) can result in the route changing. In this case, as you’ve noticed, it’s no longer choosing the return route.

It is quite easy to work around though – if you add a via point, that’ll force the route to go that way. So in this example, if you add one at Alconbury (by where the spaceship restaurant used to be!), that will “pin” the route to go that way and you should be able to then send it to a Garmin as you’d expect.

That's done it, thank you :)