There are many Top Gear shows. Make sure you use the correct name, as listed in thetvdb.com (Search - TheTVDB.com).
Make sure you follow the correct naming and structure. Plex is very picky about TV shows. See documentation linked below.
It also helps to add the year to the show name. Use the year the show first debuted, not the year of the season.
When adding the shows to Plex, since they are so close, add them separately. This may keep Plex from trying to combine the shows.
After renaming, perform the Plex Dance for the entire show, not just the episodes.
https://support.plex.tv/articles/naming-and-organizing-your-tv-show-files/
