hello. I'm Developer of Jetpack guy.
I had tested My game, then I knew there was a mistake that the Achievement is not working.
because the game build was the First Test build, not latest Version.
I'm New of Steam Publish, so I didn't know that I must Change the Build Version Manually.
I Changed Build Version lately. maybe, it would work correctly.
if there are someone that Already Completed the game, You Should Delete Game Completely And Redownload Games for gaining "Clear Achievement".
Sorry for your inconvenience, And Have a Nice Day!