The problem is caused by a lack of prediction in the `isect_line_segment_tri_v3`
that incorrectly confirms some intersections of coplanar segments to the triangle.
The solution is to use another algorithm to detect intersections.
This also resulted in a slight improvement in the performance:
- 1min 17sec to 1min 6sec in my test file
Differential Revision: https://developer.blender.org/D8500
c0340ec893