It appears there’s currently no official updates because of some issue on Thecus’ Linux Kernel.
Edit:
Just found the official note on the Thecus situation in the PMS release announcement for version 1.15.0:
Plex Media Server 1.15.0.647 is now available to Plex Pass users in the Beta update channel
This version contains numerous changes and a lot of invisible behind the curtains stuff. There a few caveats and some missing builds at this point:
Notes:
- Thecus Builds for Thecus devices will not be available at this time. Thecus is working on a firmware update that allows the new PMS to run on their devices.