3 times m rebuilding my house with the same problem.. When I make first floor it was OK.. And I stop loking at it.. But after i have my house completed without interior, I found this.. I'm going step by step back.. And at the start it was okay.. I really don't know why if I see it okay at first floor.. IDK if this bug or what.. Tahnks all of us for help

Looks like you used cfe right beside the pool? Did you? Maybe you can't do that, I've never tried

Yea I do this... U must, because.. without it u can't do underground pool.. But on the next side of pool.. It's OK.. I dn't know why this makes...

Perhaps it would be easier to just join the basement wall with the pool wall, that way you won't need to use cfe.

You don't have to use cfe, like Ayames said you put the basement wall beside the pool. I wrote this on another post

Create a pool, then create a basement right beside it, it will only work one square away. Then take the basement tool and hold down ctrl and drag the basement tool across the gap in between the pool and basement. You will be left with a wall missing and the pool, all you do is now fill in the gap in between with a basement. It's hard to explain this. That's how I do it anyway and when the basement and pool are tight beside each other I use moveObjects on to place big windows.