[2020] Problem with people stuck inside a mine

I build a mine by building ladders down several levels and then digging out rooms. This is an album with the top and bottom of the mine: https://imgur.com/a/plB8vfO.

When I select a settler and mouse over area it shows that they can walk there. It shows the same for the ladder at the top of the mine. However, it shows all of the floor beyond the ladder at the top as inaccessible. I tried removing the torch, and I also tried telling them to mine to the side. Neither worked.

Has anyone else encountered this problem?