The UK soaps have caused issues with Plex for years, mainly due to them being date based instead of Season/Episode
As you have found, the ITV soaps do not get flagged as new episodes, so you need to set the option for recording new and repeat episodes (restricing to just itv is good, otherwise you get the old repeats on itv3)
How have the recordings worked for you?, I find them annoying as it groups both the days episodes as one (so last nights 7:30 & 8:30 one will be grouped together as one episode