is one meter cube considered small in sketch uP.?

I have no idea why this one fails to work. Attached a screen record.
I promise i selected two solids to do the subtraction, and after that, the resulting object is no longer a solid, when I look carefully, I saw there is an opening in an unrelated area, making the geometry not dense anymore:
https://drive.google.com/file/d/1bqjdEAc4QHdDXUhFeM7NpLFp4qQELJ4J/view?usp=sharing

Any suggestions? All comments appreciated!

10-14 morning version.skp