What did you change in the sabnzbd setup that affects/touches Plex? The user that runs Plex Media Server?
I’ve never used sabnzbd. If you’re using it to download media for Plex, make sure the downloads go to a temporary/holding directory first. Do not download direct to the Plex libraries. That will cause problems when Plex tries to scan partially downloaded files.
Can Plex play files stored locally on the Plex Media Server?
As a test, copy two or three known good and two or three problematic files to a directory on the Plex server. Create a new library, add the files, and see if Plex plays them OK. Force a video transcode to make sure hardware transcoding works as well.
Regarding mounting the NAS…
What is the NAS? Synology, QNAP, home built, etc.
Are you using NFS or SMB for the mounts?
See Linux Tips: Mounting NFS network shares for Plex use. Note that you have to set permissions twice. First, after you create the mount point (/mnt/ChiroNAS) and second, after you mount the directories.
