This isn’t actually a big deal to me personally, as I’ll get plenty of miles to complete this mission in time. But this seems to be an ongoing issue with missions who say “all your rides count toward this mission” (but then rides somehow don’t get credited toward completing the mission.)
I thought me supplying some specific data would help track down the issue.
On Saturday I logged into Zwift, signed up for the L’Etape mission, and started riding in game. I was already signed up for two rides, so just a few minutes after I started riding I joined the start pens for the ZSUN Base Builder ride. I rode that for a little less than an hour (24.1 miles), then clicked to join the second event, the P Race. I finished that ride (35.3 miles), then saved my ride and exited Zwift.
The next day I signed onto Zwift, expecting to see the total mileage from Saturday credited toward my mission. But it only showed 35.3 miles – the distance from the second ride, the P Race.