Cannot execute xCode 9.4.1 applications

As a rule my swift codes are stopped at the class AppDelegate: UIResponder,UIApplicationDelegate { = Thread 1: breakpoints 2.4 ?? or something like.

This code is written by xCode, not by me.

I am using MakBookAir with 4 Gb memory. Full memory 128 Gb. May be problem in a small memory?

Please advice.