Oh yes. It’s the app, I’m sure of it. Even reinstalled the game to make sure.
Yeah I just fired up Altos Adventure as I have that to test, definitely not as smooth as it should be on my 11 inch iPad, even just the scroll down of the title screen has quite a few micro stutters whereas on my iPhone X I couldn’t detect any stutters, I guess their game engine isn’t the most optimised, at least for higher resolutions.