The plot thickens!
After studying Minn's post, I realise that there are two different areas/features, being discussed here. The screen shot above, is of the "light coloured" area that I was referring to. - But! - there is also a hole at the side of that area that is not visible with the lighting setting that I normally use.
When the lighting is reduced, the REAL HOLE, that Minn is referring to, does, (as she says), disappear!
..... But they are both, intended features!
Edit! ... I see that you have now added your own pictures, Minn. - Sorry!