Floor not showing in basement

[lurcher85]

I have an existing basement with ceiling height of about 6', I am doing an addition with a basement with ceiling height of 8'.
When I take a section through the basement my existing floor isn't showing.
I want to connect them with a couple of stairs (four to be exact), but can't because the existing part doesn't have a floor for some reason.
I have checked all of the settings that I can think of and can't figure it out.
I have an invisible wall separating the new from the old.
I have tried changing that invisible wall to a concrete wall with a doorway in it, but that didn't work either.
Does anyone have any other suggestions? Thanks.