How do I make an object span from the bottom of page 1 to the top of page 2

I have a shape (just a big rectangle) at the bottom of page 1 of my document. I want it to spread down to the top of page 2 so when people are scrolling through the document one page just transitions to the next. I know there's a way to do this because I did it by accident once already (see screenshot). I believe what I did was add page 2 to the spread and then use the Page Tool to drag it below instead of to the side.

However, when I try to do it again with page 3, I get this weird effect. When I try to drag page 3 below, it just turns blank. I'm not sure what I'm doing wrong or how I even made it work the first time.