Thanks to Lupp for detailed advice. But I am still having the same problem.
I am running LibreOffice 5.3.6.1 on a MacBook Air with OS X 10.12.6. I print to an HP 8620 via wi-fi; the driver was updated today with a July 2017 version.
When I print from LibreOffice the page prints sideways. Not in landscape, but sideways, so that the lower part of the page is cut off. The workaround suggested in this forum, to Export to PDF first, does work; the PDF prints properly. But this is awkward. (This problem does not occur when printing from applications other than LO, and it seemed to appear when I upgraded to 5.3.6.1.)
I have run LO in safe mode and the same problem appears.
I went ahead and removed my Applications Support folder for LO, then restarted the computer and LO. Problem persists.
If anyone has advice on what else to do, I should be grateful.