Thanks for playing!
The GUI issue is only when playing the web version not in full screen. I could not get it to scale properly with Unity 2019.
The 'right' way to get rid of ! block is by touching the less blocks of a same color possible. Normally it should only take your current coins. However a bug make it that the score also drops.
Unpredictable in what way? I know it's missing some explanation and that there are some collision bugs when rotating. However the rest always works as expected.