Can't select a shape

I am using SketchUp 2017 and I am trying to create a custom 2 gang wall plate for a Raspberry Pi based music player. I have the model mostly done, but there’s one shape I made that I need to push/pull but I can’t select the shape. When I try to select it the entire shape behind it gets selected. I’ve gone over it several times to make sure it is closed and I think it is. The shape in question is red.

2 gang.skp (1.2 MB)

The shape hasn’t quite cut the surface which is why the edge is showing darker.
Redrawing an edge usually fixes it.

Excellent, thank you! I didn’t know that’s what the bold line meant. For future reference, how did you determine the problematic line?

In the case of your model any part of that line will work, it is simply one of those occasions where for some reason the edge just hasn’t broken the surface.
Other times it will be caused by a break in the edge, that is harder to find. In those cases sometimes turning on endpoints allows you to spot the gap.