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
I've met the same problem. Finally I find out that this is because I accidentally resize the simulator's screen using my mouse cursor. By quiting and restarting the simulator my problem is solved.
Hope the aforementioned information helps.