If you set the fill colour of an AutoShape to No Fill then you can no longer select that shape by clicking on its body area; instead, you have to click its outline.
If you additionally make the line colour No Line then you still have to click the line (even though you can’t see it) to select the shape. It might have been better in those circumstances to revert the behaviour so that you can click anywhere in the shape.
It’s not too bad if the invisible shape does not fall within the bounds of an object with a fill colour, since the mouse pointer changes to a four-headed arrow as you move it over the inner shape’s border; however, if it is bounded, then the four-headed arrow appears over the whole area of the outer shape.
You might wonder what the point is of having a shape with no line and no fill. One example situation where this is useful is to create a clickable area over an image in PowerPoint that acts as a link to elsewhere in the presentation.
The only ways that I know of to select the inner shape are (1) trial and error, trying to click on its border, and (2) selecting everything and then deselecting everything else, which can be long-winded if there are lots of shapes.