I'm not sure if this is my coding or not but I can't seem to fix it and it renders fine on windows.
This is quite a severe one.
What I've done is made a level 8000 pixels wide.
I use fastloops to draw a random level adding an active as a backdrop and moving it accordingly to draw the level.
It seems to render fine until you scroll.
What happens is the first part of the window ( 800 pixels wide ) continually renders over the next part of the screen.
Almost as though it is a separate later but it is not and is slows the app right down.
I've added a screen shot to demonstrate this.
There should only ever be 1 top and 1 bottom line but the first "screen width" of backdrop constantly displays all the time and the actual main screen only renders when scrolling.