If I have a planar surface, like in the attached file, Trim with the Line option doesn’t work unless the first point after clicking the Line option snaps to something. Steps to repeat:
Open the attached file, and work in the Right viewport
Select Trim and make ExtendCuttingLines=Yes ApparentIntersections=Yes
Click, without snapping to anything, to create a cutting line and select the part of the surface to cut away.
(To make it function as expected, do the same except snap the cutting line to any part of the surface.)
apparent intersection fail.3dm (29.9 KB)