There are known issues with DVD order using the TVDB v3 api.
Two solutions:
- Switch to the “Plex TV Series” agent (we’re already using v4 there).
- We’re rolling out the updated TVDB api to the legacy agent over the next few weeks. This will require PMS 1.24.5 which is currently in beta but is also a staged rollout (see here for more: TheTVDB agent - v4 update)