I had a similar issuer as elidoran. I thought i did the list above and I was at 20 of 22.

I hand Olympian for all beginner tacks except for hard on Space Trucking and Roswell. Got hard on Roswell and it went to 21 of 22.

But i decided to double check the list an saw I did not do Portal. I completed that on Easy and then I received the Achievement.

I did not do castle on Easy but on Medium not sure why that would matter but. There is a bit of oddity to the Achievement.

What I did was work through this list one at a time doing Easy mode with Ten and Reverse options on. After beating the last on the list, Bloontonium, the achievement didn't pop.

I went on to do special mission achievements and some others over the next week. Then, I started beating Easy/Medium/Hard on each mission with an Olympian achievement, starting with the Beginner maps. The day I did Roswell and then Space Trucking i received the achievement immediately upon completing Easy +Ten +Reverse on Space Trucking (I hadn't played it before).

When it didn't pop I went over the list a bunch of times to ensure I had played each one on this list and I was missing two somehow. All the game, and steam, showed was 20 out of 22 instead of showing which ones were completed and which ones were needed, of course. Be great if games would start listing what's required so we didn't have to figure it out via trial and error.

Can confirm, Impoppable doesn't count towards this achievement.

In case that is the source of the issue, I'll update the guide to specify that only easy, medium, and hard medals count.

Did you only get the impoppable medal on some of the tracks? Impoppable mode was added in the 2.8 update of the mobile version (before the Steam release), so it's possible that the achievement for all versions of the game, including Steam, doesn't count impoppable medals.

I'm relatively certain that my list is correct, as I cross-referenced my own progress with online resources on Steam (post #11) and AStats [astats.astats.nl] and found that they concurred.

I think this list is incorrect. I beat all these and Steam said I had 20 of 22 needed for the achievement. It wasn't a matter of waiting a bit either because I continued playing for over a week after that doing other maps and achievements. When I went thru to get Olympians on all the Beginner tracks I finally received the Track Star achievement after beating Space Trucking and Roswell before that in one game session.