On DSM 7, the plex username is abandoned. Synology forced the change.
You may delete user plex.
The new username, which has a new shared folder, is PlexMediaServer.
DSM 7 introduced a ‘System Internal User’ class for apps. We were forced to abide by the new rules.
Look in the Syno FAQ.
There is a DSM 7-specific section
Did you “click right through” the “Installation Successful” message?
