Server Version#: DSM 7.1.1-42962 Update 3
Player Version#: 1.31.0.6654-7000
Some time ago, my Plex installation lost access to see any of the local files. I confirmed the permission was set correctly, but I cannot get the option to add the media back. At the time, I was running DSM 6, so I decided to upgrade to DSM 7 and wipe the NAS, thinking that may help.
That is an error we are looking into, we think for some a process is not starting up correctly. For some folks restarting server on machine has worked.