Oh. I got it.
Yes. This bug occurs on all iOS 8.4 beta. However I can say this bug still exist because I have an overall worse result of that game while my skills doesnt change a little bit. To be more specific, when I try to tap the screen to respond to incoming rings, I sometimes need to tap twice, which is surely impossible in the game.
And when I want to launch an app from home screen, whether in portrait mode or landscape mode, sometimes I need to tap app icon twice to finish it.
I have heard that iPhone 6 Plus resolution result is a constant downscaling process. I don't know if it is really true, but when I see screenshot properties, I don't see 1920 by 1080. Instead, I see 2208 by 1408 or some other value, which is larger than 1920 by 1080. Could I guess this is the reason why iPhone 6 Plus screen sometimes becomes unresponsive in safari.
PS: all what I say occurs on iOS 9 beta 1.