Where did you find the return single ticket offeted on the app?
Did you reverse the reverse the departure/arrival stations and buy a second time? How easy would that be on a TVM▸ ?
The app offered two options, a return and two singles. It must have remembered in the settings that I had a network railcard as well as when I printed the tickets at MDW this morning the return leg was marked "
NSE▸ ", which I hadn't appreciated at the time of booking. Luckily I still had a week left on the railcard!