Hi Zwift, I finally had time to ride the (amazing!) Alpe du Zwift. But, for some reason I didn’t get a star for turn 20 (in the beginning) so I ended up with 20/22. How is this possible??? I climbed to the top! Where is my reward!?
Besides that, I really enjoyed the ride, but it will take me some time to recover before I can climb that mountain again 
Hi Peter. Frustrating after all that work. Happened to my friend the other day as well.
He runs his Zwift off of his Iphone to TV. The only thing we could think of that would cause this is a massive internet drop. He took a couple of calls while riding.
You would not notice as your avatar would keep going. All of the surrounding riders would have disappeared temporarily.
You could use https://zwiftalizer.com/ and have a look at your ride file. You can watch this video to learn how to do this. PC or Mac, I believe.
If you make a U-Turn on the way up (even if it just for a short section) you will loose a star, you will need to go down to the previous star and re do the whole segment.
Hi Norm,
I raised a ticket after the same happened to me, see the response.
Hi Gerrie,
Thanks for reporting this. Our QA team has also found this. They have also informed me that if you go to the beginning of that segment and complete without the u-turn, then your star will reappear.
Let me know if you have any other questions.
Thanks,
Josie