No matter how I name them, not a single part of a tv serie, from dvd, is shown in Plex

[tom80H]

So… how did you name them?
I assume you’ve added the files to a separate tv-show type library?
Have you verified the Plex Media Server on your Syno has access to the files (this will depend on what version of DSM your Syno is running)? → Synology FAQ - Questions, Answers, and How-To's - #25 by ChuckPa