I used to be able to offset all types of curves seemingly with no probelms, even if they were complex/not planar. Now suddenly any curve no matter how simple, has strange loops at every corner. I assume there is some setting that caused this. Trim is set to yes and doesnt make any difference.
Likely cause: The input curve is not planar, or is planar but not parallel to Cplane. If it is planar then use InCplane=No. (InCplane=Yes means each point on the offset curve is offset parallel to the Cplane. If the input curve is not planar and parallel to the Cplane then the offset curve is not planar does not intersect.)
If you are offsetting a curve on a surface or edges of a surface then use OffsetCrvOnSrf for the offset to be on the surface.
You might have some luck with the “inset” command if you’re really having a hard time. If the face is in fact planar you’ll be able to MergeAllCoPlanarFaces to get rid of the extra edges after you copy them in place.