Impossible to say without knowing what constraints are in place at runtime.
When you use Xcode’s view debugger, what does it say about what constraints are active? Do you have auto layout warnings in the console? What are the dimensions of the main screen that the app sees? (Maybe target B doesn’t have the right launch storyboard or images)
Could you explain as well what Target A and B are ?
Is it only on simulator or also on device ?