In Plex, the UK (without-suffix) and new US (with suffix) are being combined in "Lego Masters (without suffix).
I contacted Plex first and they looked it up via the API:
https://forums.plex.tv/t/plex-only-dete ... u/538861/3The API is only returning US (with or without “US” suffix) and “AU”.
Please bring this up to TheTVDB folks. It is an upstream database omission.