That’s because 5.7.3 infuse introduced Plex on deck to start watching the next TV episode.
On deck unfortunately is not integrated with the the up next list but a separate list (on deck) on the homepage, on deck also does not show up on Apples Top shelf. I remember infuse mentioning they had a problem integrating on deck to the up next list therefore made a separate list.
One tip I can give you, although not elegant for starting the next TV episode from the up next list, is if you watch the next tv episode for a second then stop it the TV season should then pop up on the up next list so the next time you want to watch that TV season it will be there.
But right now with Plex integration to start the next TV episode you’re supposed to use the on deck list on the infuse homepage.
Using smb or nfs uses the up next list to start the next episode just not the Plex integration.
Personally i think infuse should add an on deck category in the up next list like recently added.
I know you might not like it but I Hope this help.