Even if this is not the first threas about.
Yesterday i spend 6 million gold and 600 gems for scratch by upgrading due to frozen screen.
Sometimes the sreen is frozen (an epic boss or orbs may come) and you try to collect gold, check timing.
If you think you have missed the point and try it again, both pushs count and as the upgrade bottom may be just under the the same position as the collect position was, you buy it by fault.
Means i made a library upgrade to lv 8 and finished it with gems due to this stupid frozen screen which counts commands in the background.
I had this in the past some times and wrote to the custumer support without getting something back.
As this is a common problem, please solve it for all of us.