I upgraded to Ubuntu zesty a few days ago and had to reinstall lyx and some packages from texlive. Everything functions as before, except, all of a sudden, pdf output in landscape mode is broken. The text is disposed correctly, but the pdf page size is still 8.5x11 portrait. So you get a pdf file (viewed with evince as usual) with much of the text cut off and white space where the page should have already ended. I do not know how to troubleshoot this problem. I've already purged and completely reinstalled lyx. There are no errors in the logs. I've tried adding the usepackage geometry, landscape. This document worked just fine before upgrading to zesty.
UPDATE: Minimum example:
• Memoir Class • Fonts via Xetex • Landscape Layout • User Defined Margins (.5in. for all - .25in footer)
If compiled using Xelatex it is broken:
If compiled using LuaLatex it works: