Section Line(s) disappear in vector export (SU & LO)

[howdy]

hello all,
having some trouble exporting sections to vector formats (pdf, eps, etc) in version 7.1---Some lines seem to disappear at random. I have read about not using "sketchy" styles, so I'm just sticking to the defaults (hidden line, etc). This happens both while exporting directly from SU, and also while in LO using "vector" moode --see the attached image for an example. Seems to happen on both Mac and Windows machines.

Any tips much appreciated!
LML

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[TIG]

Try using SectionCutFace ruby first...