I came across a strange problem when using on-screen keyboards both on a Surface Pro 3, as well as on an iPad. In the case of theiPad, in a large multiline text field, there is a significant delay from the time you start typing to the time when the text appears on the screen, this only happens when you first load up the screen, subsequently it returns to normal behaviour.
The same thing happens quite often with a Surface Pro 3 (on-screen keyboard mode), at one point when I closed the on-screen keyboard, the portion of the screen that was previously covered by the on-screen keyboard was completely blank i.e. white. Even when I exited the app, the Power Apps studio also only showed half the screen.
Unfortunately it did not occu to me to note the session details. i'll do so if it happens again, but the screen delay happens quite often when typing with an on-screen keyboard.