Exactly this - even if trip.com reduced their railcards to a fiver, I'd not bother and stick to one from a retailer I trust. Way too much risk that I'll be caught out unable to show it.
I bought the discounted 3 year Senior Railcard from Trip.com. I’m frustrated that I can add tickets to the Google and Samsung wallets but not the railcard.
I tested it for offline use and discovered the following:
Signal is required to access the ‘account’ section of the app, so if you’re opening the app at the time you’re asked for the railcard and you’re offline you’re screwed.
However, if you access the ‘my railcards’ section when you do have a signal and then go offline you can still open the railcard and the colour changing logo still appears as it should.
So the simple workaround is to have the railcard displayed or at least be in the ‘my railcards’ section of the app while you have signal and just leave the app open in the background during your journey.
Not perfect but it solves all these extreme scares about prosecution etc..