I am rather new to SolidWorks and completely new to sweep.
I followed the sweep training path on MySolidworks and then jumped in to make an example of my own.
If I used only profile and path, and the path is in 2D, it is ok.
If I am adding a guide curve made (manually) in a 3D sketch, then after the end of the 3D sketch line, it goes back automatically to the origin, and all lines from my profile converge to one point. I even had to disable 'merge smooth faces' to have a picture that is not a preview.
I revised by profile and checked my relations, including where the 'pierce' is set, without success.
I have attached my part. I am running SW 2018.
I edited the end of my 3D sketch and it modified the beginning of my sweep.
I attached that part as sweep_fail2.