Just manually updated to PMS 1.15.8.1163 on Synology DS918+, and the Plex share priviledges were reset back to default. It’s no big deal because it takes no time to switch it back.
I do have a question though…is there some technical reason why the Plex media should be on a separate share than the metadata one? I didn’t really want to have two separate Plex shares on the NAS, so I setup the library folders on the metadata share. Seems to be working just fine.