I have recently updated Xcode to version 10, and now my console displays:
MyApp[1618:133310] [AXMediaCommon] Unable to look up screen scale MyApp[1618:133310
It could sounds dummy, but these warning appeared me after move the simulator previously rendered from the Macbook screen, to a wider external screen.
I solved it just restarting the simulator in the external screen. My 2 cents.