It is a separate show not season 4 on TVDB and moviedb. Nexflix calls it season 1 as well
You should be using S01E01 not 1x01 but other wise naming looks fine
You have colons in some text there so not sure if you have them in file names but should remove them if they are there.
If you have been renaming them a bunch trying to get it to work you may have to do this to clear cache The Plex Dance ™
