I have noticed that the button controls on my main screen work fine until I navigate to my second screen which has Text Input boxes and I enter text into one of them. After doing that the buttons start playing up both on the screen with the text inputs and back on my main screen which has none. The buttons will press and carry out their OnSelect action however they get stuck displaying the button pressed colour so it looks like you are continuously pressing the button. You have to tap them again quickly to get the colour to change back to the normal fill colour. I have to shut down and re-open PowerApps to get it to stop. But as soon as I use a text box it starts again.
This issue has already been reported in other posts several times on this forum over the past few weeks but no response from Microsoft yet as far as I can see. @DerekPapworth
A bug like this is a show stopper for my PowerApps clients. If this is not fixed quickly PowerApps will have to be dropped in favour of a more traditional and reliable approach to building apps for mobile devices.