Server Version#: 1.25.4.5468
Player Version#: 4.73.3
I migrated my PMS from a Mac Mini to a DS920+ running DSM 6 and then upgraded to DSM 7. Somewhere along the way my external and managed users lost access to my server, even if they were on the local network. What was odd was the user could see that I had shared the libraries under “Home & Library Access” but it didn’t appear on the home page. I believe it happened after the Mac to Synology migration but I’m not sure.
I followed these instructions to migrate from Mac to Synology, but I probably should have followed the official FAQ instead, as the FAQ version recreates the identifiers rather than modify the XML directly.
After finding many closed topics on this site, all with the same issue but no resolution, I tried a few things out and finally fixed it! Note that the share permissions were correct, with the local PlexMediaServer user correctly having read/write access to the shares referenced by each library, so I knew this wasn’t the issue.
I made a copy of the PlexMediaServer share, did a complete uninstall of Plex, manually installed the latest version of PMS for DSM 7, created a managed user and library and found the user could access the library, both on local network and remotely.
So next I tried restoring my ‘faulty’ config over the top, so shut down PMS, restored my backup of the PlexMediaServer share back and started PMS. As expected, it still didn’t work…
I then tried the steps in FAQ 22 - When server and device credentials are out of sync and BINGO, managed and friends can now access their libraries! 
