This happens on my iPad too, I have one possible explanation. Your finger is on the screen but the main pressure point is outside the edge of the screen. To understand what that means, you need to be aware that apple has designed the iPad to ignore touches from the very very far edges of the screen because it sees it as incidental touches, as in holding the iPad and your fingers are wrapped around it for support, they could touch the edges of the screen and disturb the flow of your work (or your movie or book), so apple designed an algorithm to ignore these touches sometimes and register it as an accidental touch. Sometimes though, in very cases, like in infinite flight, the algorithm can register touches that are intentional as accidental, because people who designed the algorithm didn’t put in mind that some of us will be using rudder controls very close to the edge. The best way I found to work around that is to control the rudder a bit from the top (away from the edge). Try it and tell me if it works.