Season 8 of the Graham Norton is messed up because Sonarr is ‘confused’ about the episodes.
This has to do with the fact that halfway during the season specials are being broadcasted, and depending on if you mark them as regular episode or not you’ve got one episode more ore less.
Sonarr now has one episode less. Most meta data providers (tvmaze for example) mark the episode that Sonarr marks as special (Season 18, episode 13) as regular data, but tvdb does not. On thexem.de this issue is visible, but for some reason Sonarr is still confused.