My door frames which are sweep1s with two closed curves nearly always have errors in the render mesh. I must be doing something wrong. This seems too basic to require screwing around with custom render meshes. Example attached with source curves.mesh error door frame.3dm (262.9 KB)
This is coming from internal G1 (tangent) composite surfaces. Unfortunately, Sweeep1 does not have the setting to not create these kinds of surfaces from joined tangent curves such as your profile. You might try DivideAlongCreases with SplitAtTangents=Yes to remedy it after the fact.
HTH, --Mitch