Thanks for playing and the feedback!
Regarding the problem you had on Level 3 did you try to freeze the virus (F) over the platform? If you did then it might be a bug but you should stay in the platfrom if you did freeze the virus. Also, if you get stuck you can always go back to the main menu and after that you get directly to the level selector.
As for the platforms getting behind frozen areas we show on the top row of the first level a cannon shooting bullets through a previously frozen area to show that, but it's probably hard to miss because you don't interact directly with it, it's just a sample.
Hope you liked and enjoy the other levels if you play them!