I passed level 193 with 3 stars but cannot advance to 194 as game does not respond at all. Every now and then a key appears with a timer but I have no clue what to do with it. The game does not let me even move to any of the lower levels.
Hmmm... you can't move forward or back? Could you send me a quick screenshot of your game map so I can have a clearer idea of what's going on with your game.
The key that's set a couple levels ahead of you will fit into a locked box which is even further ahead. If you reach the key and the box during the time you've been given you get rewards. If not the key will fly away but don't worry you get another chance soon.