I’ve got a hull surface with a horizontal crease. Splitting or trimming the surface using a planar surface or line at exactly (= within document tolerance) fails. Using the command ‘Intersect’ reveals that a part of the expected intersection curve is missing.
Trimming or splitting using a cutting object that is slightly above or below succeeds.
I’ve prepared a file that I can send in a PM in order to check whether there is something broken in the surface or in Rhino…
I hope that this can be looked into.