I have been experimenting with Windows touch screens and there is a noticeable jump / drop in framerate when the ‘input touch’ node is triggered.
This is reproducible in 4.17 by creating a new blank project, setting up an input touch node in the pawn and observing stat unitgraph whilst tapping the touch screen. I have tried this with a few different Windows touch devices and the judder is always there. It looks like processing the touch causes the game to pause a fraction of a second.
This was not present in 4.14 where the mouse cursor emulated touch.