My terminology is a bit rusty so bare with me. I have designed steps with paths, were I want to subtract a 1mm radius half circle arc on all the surfaces following a path.
The problem seems to be that the arc surface is following the line, but not taking in account that the arc will need to rotate along this own axis to compensate changing directions in 2 axis.
When I do this the first surface works fine, the second does not and it just gets worse the further the “Follow Me” tool is used.
Personally I would have liked to use a circle and used the follow me tool and then just deleted the rest, unfortunately it wont let me do that either. It tells me that it cant extrude a curved surface.
You might try this. Copy the path to the side and use the follow me tool to extrude a round shape. I would recommend reducing the sides to something under 10. Then move this tube back into position and intersect with the stairs. You will have some cleanup to do. And as Anssi says, scale this up to reduce the number of small face problems.