With mobile tickets I've also lost the ability to break my journey up (i.e. visit somewhere half way along a route without having to buy two tickets) which has increased the price of my journeys.
I tried to use an off peak QR code ticket and it did not pass the gates and I was told I wasn't allowed to do it, the ticket rules did not mention it either.
It is possible the staff just didn't know about the break in journey rule, I was too tired to fight it at the time.
Yeah, I missed my outbound Air Canada flight at LHR after my coach broke down and when I asked about getting a ticket for a later flight, the rep told me that they "weren't supposed to" sell returns if you weren't planning to use both legs even though they were cheaper than a single but she sold me one anyway, just told me to make-up a return leg and then just don't turn up!
Pretty bad really, I guess an example of where the theory of balancing the numbers doesn't match up with the reality that is obscene that they can gouge you for less service, I think it should ultimately be "admin overhead" + "flight(s)". Most people accept that a single can't always be half of a return but it should always be noticeably cheaper.
Yes, airlines will typically cancel the whole trip if you just don't show up for the outbound leg.
I have, on rare occasions, not shown up for the return flight because just buying a new one-way ticket for a new date/time was cheaper than rescheduling the existing return leg. I don't think you're actually supposed to do that either.
Our ticketing system is so incredibly complex, and train companies aren't always interested in educating their staff, so unfortunately very frequently the staff get it wrong