Actually the bubbles not colliding is a bug, it occurs when one of them touches the edge of the tube. I know about it and tried to fix it but nothing worked. I even think this bug is happening on browser and not on my machine, maybe I'll patch this in the future.
And yeah, the game is hard. It's addressed to people already familiar with Suika Game who already know how to score well. I could balance this by making the numbers more sparse, currently it's 1/8 ball can have a number, with the first one forced to have one.