Was running into this issue in another model trying to do the same thing. So I created this file to verify the error. Just a simple 30"x30" square. I turned on color by axis to show the geometry is all aligned.
Steps:
Drew the square perpendicular to axis.
Drew the line from bottom right corner 30" back as reference for arc.
Drew pie arc to connect typing in 90º to be sure and checking snap inferences.
Select arc and click Follow Me and select face.
Result is shown with stange anomaly at the bottom and the non- perpendicular follow me faces.
This isn’t an error with Follow Me. Follow Me is doing exactly what it is supposed to do. Follow Me requires that the profile is perpendicular to the first segment in the path. If you don’t set that up, Follow Me projects (it doesn’t rotate) the profile perpendicular to that first segment. The extrusion will end perpendicular to the last segment in the path.
For the sort of thing you show, you can either extend the arc a bit with straight edge segments that are on axis or, the thing I tend to do is create a path such that the first and last segments are on axis. That is easily done by starting with a circle and rotating it so edges are on axis. Then cut out a quarter of it for the path.
