This is all a classic case of several factors, each on its own understandable, predictable, appropriate. But when they combine together exactly the opposite is true.
1: Expectation and encouragement for passengers to pay their fares by self-service, to reduce the costs of ticket vending
2: Requirement for passengers to buy before they travel
3: Punitive enforcement action against those who do not pay.
But 1 + 2 alongside 3 is reliant on a piece of technology that is not in itself covered by any of the rules or terms. There is no account taken of the possibilty (however rare) of an electronic device failing, whether through flat battery or otherwise. Thus the perfect storm is that a wholly legitimate passenger who has caused the Railway no loss whatsoever may still be subject to punitive action when the cause is at least in part beyond their control.
For myself, I will always buy in advance (for an Advance fare) or on the day at a TVM or office (others) and any ticket bought at home will, without exception, be printed, so I will have two copies of it with me; the pdf electronically and a paper copy. Now frankly, that should not be a necessary precaution, but it is.
Failure to produce in the case of failed electronics needs to have proper provision made for it in procedures. Customer later provides a ticket and no punitive action is warranted. Case dismissed. The unique barcode will identify the ticket and should/could indicate whether it has been used (by another or on another occasion). And if the "system" can't record use, then it is the "system" that needs investment.
The Railway can't morally/legitimately "have it both ways" yet it persists in doing so. Sure - save vending costs by Electronic Ticketing. Sure - penalise those who don't pay. But don't penalise those who do pay all that is due, but can't prove it on the spot.