I just recreated that little wiggle in the surface that you show... I created the 2 circles and 3rd tangent circle then trimmed.. Then mirrored to get a closed curve.. I swept a circle along this path and all looked well.. I selected "2 profile circles" and swept those along the same path and got the wiggle in the same place you show there...

Are you changing profiles dims along the sweep? If not, just use one profile circle for the sweep.