I am not sure whether is it cordova's issue. I have not got the chance to test it out.
stackoverflow.com/questions/46232812
/cordova-app-not-displaying-correctly-on-iphone-x-simulator
I'm not sure if it's C3 or Cordova because we are getting inconsistent results, a few of us are having this viewport shifting of the screen problem but others like Kraudi released a game last month that displays correctly on iPhoneX, but he gave me a blank project with all the settings he used for that game and it doesn't display correctly for me but it does for him.