I'm on that list of journeys page (eg. https://cycle.travel/by/alexs77/journeys?group=13751 — link might not work for you…). When I click on the download button, followed by "More download options…", I see this:
As you can see there, both the GPX route and TCX course options are deactivated.
When I open the journey on the map screen and then click on the GPS button -> More download options…, both options ARE activated.
Why is that so? It should not be like this, in my opinion. Either that option exists (as on the map), or it does not (as in the list).
Comments
The technical reason behind this is that TCXs (and GPX routes) include turn-by-turn instructions. If you have a long route, cycle.travel won't generate these by default (to keep response times quick) and therefore they won't be saved with the route. The journeys page isn't able to generate the turn-by-turn instructions, and so it can't offer a TCX course for download.
It's not a hugely easy thing to fix I'm afraid but I agree that it could be explained better – I'll look into doing that. And thanks for spotting both of these!