I have this shape. The upper segment has the same profile as the lower at the front.
Now I want to fillet and I get this.
The big fillet radius was too big so it completely consumed the front surface.
See where the font edge goes to a zero width? There is no mathematically rigorous solution for those surfaces and that radius. Try it again with a slightly small radius that does not drop to the bottom of the surface edge.
Thanks. I am still getting unbelievable weirdness even with very small radii.
I am thinking I will have to build this part differently than on on the system from whence it came.