Permissions issues on DSM 7

Is the Plex user account still being used by PMS? I’m having issues deleting movies I’ve watched through Plex when I transfer them to the Synology using the Plex account. I was assuming that it was because the new PlexMediaServer internal account didn’t have R/W permissions on them.

It happens when I add new movies to the Synology through the LAN using the Plex user account.
This use to work fine before, when PMS was using the Plex account for everything, but since DSM 7 it stopped working and I was assuming it had to do with the switch to using the PlexMediaServer account (which I can’t use to authenticate over LAN since it’s an internal account instead of a local user). I’d love to understand how PMS on DSM7 functions to work around this issue.

Corentin