Good thing this has game save ability, because it has pretty bad lag especially in some of the later levels.
You can refresh the game and this helps with the lag a bit, but also sometimes the game penalizes you by a few levels which you'll then need to repeat to get back to where you were.
I didn't find the medals to have any issues, but sometimes the game itself isn't saving what stage you'd gotten up to, especially once the lag sets in, and will be one or more stages behind. It was a full 3 stages behind in one case.
And that's a problem in some of your otherwise decent games is the lag! Perhaps have one single music instead of transitioning the musics (or at least don't transition while in a stage), and perhaps reduce the amount of animated objects in use at a time. There are other techniques to reduce lag as well but some of it is just up to the platform you use, but there are definite things you could be doing.