Hi Mala,

re:
> Here's a relatively simple geometry. Here, too, the sweep is twisted.

If you make a sweep with just one profile at the start, it will reduce twisting in the generated sweep, like this:





Compare the end with "natural" twisting with the 2nd profile that you are using:



Basically your 2nd profile is at a pretty significant rotation away from the natural sweep result.

When there is a fairly large rotation from the "natural" position it can make things difficult for the mechanism that determines if a profile needs to have its direction flipped and also which segments should be connected with each other.

One way to solve it would be to add an additional profile in the middle. When there is a smaller rotation happening between each profile station it will help the automatic seam and flip detector work better.

Another way which is probably easier though would be to only do a sweep between a single profile segment instead which will eliminate segment matching and you can fix the wrong direction by using the "flip" command after the sweep is done.

So for your case here, select your profile curves:



Run Edit > Separate to break it apart into individual segments:



Select 2 of the segments that you want to be matched:



Run Sweep on those:



Finish the sweep and then correct the wrong direction by selecting the 2nd profile and then run the Flip command - type Tab then type Flip and push Enter. That should get this result:



Repeat this with the other profile segment (the line), then select the 2 pieces and use Edit > Join, then select the object and run Construct > Planar to put end caps on.

Result .3dm file is attached.

- Michael