You have a permissions issue where the server is not allowed to see the drive/directory
May 20, 2019 18:18:03.970 [0x7f7babe80740] DEBUG - * Scanning /volume1/MOVIES/R May 20, 2019 18:18:03.970 [0x7f7babe80740] ERROR - Couldn't check for the existence of file "/volume1/MOVIES/R": boost::filesystem::status: Permission denied: "/volume1/MOVIES/R"
There was a recent change in the server for Synology. Info on the changes and info on how to change the permissions so the server can see the directory/shares again can be found here Plex Media Server security changes for Synology users
