Annoying

I thought I had found a great new game for my iPad but it keeps freezing after I have left it for a while, Or when I have just completed a puzzle then when I do as someone suggested and turn the app. off and restart it, it begins at the beginning again and I have to go through all the puzzles again to get to the level I was at.
I am using the free app. is that the reason?

Emgeebee about Trainyard Express, v1.66