I had to restart my iPad due to connection issues and killed the Zwift app in the process. When I restarted Zwift, I was happy to see that the app recognized that I had the partial activity left over and was able to pick it up where I left. I was at the correct position on the map, with the correct mileage and time counters.
Even though the app also recognized that I had been riding a route (Accelerate to elevate), the progress along th route progress was reset to zero (see screenshot).
Also, when I approached the junction where I had to go left to Alpe du Zwift, the app had preselected to go straight on to the Jungle route.
When I then selected the left branch to the Alpe manually, the route progress indicator on the screen had disappeared. So the app was of the opinion that I had left the route. Therefore, I also did not receive the route badge when I finished the climb.
It’s really nice that the app can pick up the partial activity after a restart, but from my POV this is a bug in the continuation of the previously selected route, in that the route progress is reset to zero, the navigation at junctions is incorrect and ultimately the route is not considered completed when in fact it is.
Here are the screenshots of picking up the left-over ride, and of the inconsistent progress (km and time correct, route progress incorrect):