I installed iOS 8.3 about a week ago when it was released and I went to use GarageBand today and experienced a problem. When trying to use any of the touch instruments, a single tap in the instrument area does not register. VO still seems to think I need to double-tap which does work. I experienced the same problem when using the Korg Ikaossilator app as well as when trying to play Audio Defence. In all of these cases, I am unable to touch the screen to perform any actions in the game. I had to double-tap to shoot in Audio Defence. I am just wondering if anybody else is experiencing this problem or if it is just an issue on my end. This would be a big oops on Apple's part if this is an 8.3 bug. Thanks,
Had this problem with another app. Try using the rota in the app and see if there is a setting for "direct touch" and then use the rota to enable it. That may work.