That’s the bug I found. Perfect.
The new installer (most likely in the next build you see), will remove the file from /etc/systemd/system
This all came about because the initial releases of Ubuntu 16.04 placed them in /etc/systemd/system which was non-standard. They’ve since complied with standard but, until now, the LD_LIBRARY_PATH hasn’t changed so the error went undetected.
To avoid any confusion,
/etc/systemd/system/plexmediaserver.service.d/override.conf is the accepted standard and supported location to customize your Plex configuration.