There is a problem following the tutorial. Could not find a solution.

Hi guys.
I just starting the Unreal engine, follow the tutorial.

  1. When the light map is built, the red circle appears to break off a little bit like a crack. Can you tell me the cause and solution?
    Is that the right solution if you set up a little bit of overlap for my friend?

  2. In the tutorial, when you edit a geometry, you can select a face and edit it, just like the image, but it doesn’t work.
    The tutorial video is version 4.7 and my one is 4.21, right?
    Has the geometry editing changed as the version changed?

I just start study unreal engine and english is not my main language, but I hope you understand.