make sure that only the immediate “parent” folder of /Cold Feet (1998) has been added to the library. Never add a single TV show directly to a Plex library.
Always use 2-digit numbers for season and episode numbers. Unless there are 4-digit seasons, or the number of episodes within a season is exceeding 99.
make sure the hosts file does not contain any plex-related addresses
in the episode file names, place the episode title after the SxxEyy code
The hosts file is a relic from the earliest days of computer networks. Nevertheless it exists in every operating system. hosts (file) - Wikipedia
Switch your tv show library to “Episodes” view mode.
Then engage the “Duplicates” filter.
If there are any episodes listed, (and you know there should be not several versions) then take a look at the plex media info of these episodes.
Perhaps the show has been mismatched and merged into a different show.
It has appeared now, after clicking “Episodes” it appeared. Clicking back to “TV Shows”, it is still there.
I am not 100% sure, but I think the problem was solved by using the double digits in combination with perhaps some caching of my browser (delaying the view).