I created a bug report (#18372) for the X11 crash. A work-around is to not call renWin.GetScreenSize() until after iren.Initialize().
The ghostly diagonals look similar to the ones reported in #18064, but that report was against VTK 9.0, not VTK 9.1. @cory.quammen are there other known issues with EdgeVisibilityOn()?