I though this might be due to a corrupt file in my last version of backup hence decided to do a new install and restore an older backup. In doing so, I found that the problem was not due at all to my library as it is reproducible on a new, totally virgin install, see details here: Plex Media Server does not work anymore, even on new install.
Hence, there is a much broader issue on Plex and Nvidia Shield that prevent Plex Media Server to work.
