Glad you have it working.
One question: Did you install the beta version from the Synology Package Center, 1.21.0.3744?
If so, consider updating to the current version available at https://www.plex.tv/media-server-downloads/. It has the latest bug fixes and enhancements.
When you install the current version, it will create a shared folder, /plexmediaserver, and move the Plex data folder (the old /Plex folder) to that location. See the “Packaging 2.0” document for details. Depending on the amount of data, it might take some time to perform the migration (minutes to hours). Don’t stop it, just let it run.
DSM 7 - Packaging 2.0 (PMS 1.24.2.4973) - Release information
Hope you & yours have a Merry Christmas and Happy New Year as well. 
