Unable to select all vertices in "Top" view mode

Hello!

I have created a hallway using ProBuilder.

I need to move a wall now.

To do that, I changed to "Top" view mode and draw a rectangle around the area that I want to move.



However, no matter what I try, I don't seem to be able to select the vertices reliably.

Here is what it looks like when I switch to perspect view.

As one can see, not all vertices are selected. If I move the vertices now, it looks akward.



How could I select the vertices reliably?

Thank you!

 

I believe I solved it using "Top" by right-clicking the "Top" instead of clicking the axis icon.
And then using the "Vertices" mode.

Even though I thought I tried that before it worked now.