Good App if keypad doesn't go blank – Math Fact Master Review

This app appears to be well designed conceptually but every so often the keypad numbers go blank as you press those numbers and then you don't see the numbers anymore unless you start over. This happened on my new iPhone 6s over and over. I'm very disappointed and don't know how to contact the developer to correct the problem. TipTapTech can't be found via Google.
Review by Redbaron747 on Math Fact Master.