Red shape and shape changing of 3D FDTD simulation zone



I’m working on a project on FDTD. I’m getting this red shape when I’m doing some modification. I would like to know the meaning of it.

When I delete everything of my project, I obtain that.

What does it mean? Where does it come from?

Another question:
When I’m trying to change the “x axis” shape of the 3D FDTD simulation zone, it doesn’t work. Why? I can change the shape of everything else in my design.




Can you upload the simulation file to help debug your issue?

Best Wishes,