Something still looks weird to me… I can’t reproduce your result starting with plane intersection.
Why would a full ellipse need to be revolved ‘0 To 2*Pi’?
Seems like 180 degrees (‘0 To Pi’) should be enough?
P.S. OK, I got it to work by using YZ for intersection which yields one half ellipse curve, which can be rotated ‘2*Pi’ (360 degrees) to give a surface that works fine with Project and other tests.
PROJECT_TO_BREP_R7_vs_R5_2021Jan19b.gh (14.8 KB)
Using XZ for plane intersection yielded two full ellipse curves. Rotating one of them 180 degrees (Pi) didn’t work.
Bottom line was that your “bad” Srf was likely created by rotating a full ellipse ‘0 To 2*Pi’?
This interruption to the forum while trying to edit this post DROVE ME MAD!!! until I finally noticed the message:
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