I'm on the GWR^▸ (Great Western Railway) website attempting to book tickets to travel to London on Sunday 27 June and back to Evesham on Tuesday 29 June.  Its for my brother's inquest - a journey I'd rather no be making.  GWR doing their bit to dissuade me

The first set of fares gave me something like £56 return fare, with the outward journey all day on the Sunday.  I selected a time of travel and, woosh, the screen blanked and was eventually replace by a "sorry there was a technical error" message.  Tried again, and, abracadabra, the return fare is now £112.40

I shall travel instead from Warwick Parkway on Chiltern, for £52.80 return and the GWR can carry my empty seat to London, earning nothing.

This may possibly be related to the original observed vanishing act - though it seems a bit unlikely for a direct train to Paddington. However, for anyone wanting to book to Marylebone changing at Oxford to a Chiltern service, that was impossible yesterday and is still giving trouble today.

There is a thread on railforums about pathologically miswritten easement, which was:
The "via" stations can come in any order so this bans any use of Chiltern trains from Oxford unless you start from there. It's not clear what circuitous route is was trying to stop - but whatever it was, it was wrong. The code on the data feed went further, specifying Oxford as via or to/from - and all journey planners should have obeyed that! So that was even wronger: barring direct trains to MYB^▸ (London (Marylebone)) too. (Though arguably the OJP^▸ (Online Journey Planner) should always allow those and not even look at easements.)

Presumably that easements file was loaded yesterday (or earlier for activation yesterday), and there was another one today in which that easement has disappeared. But loading the file takes time, and I think is done overnight, probably with the OJP offline.

As of tonight, the NRE^‡(resolve) OJP still can't find a valid ticket using Chiltern. Even when told to avoid Paddington, it routes to there and on to MYB. It does not offer through tickets either, though there is a one-way fare, that is unlikely to be meaningful, as it also complains:

The GWR^▸ (Great Western Railway) OJP finds a super off-peak at £62.20, which I think includes the Tube PAD^» (Paddington (London) - next trains)>MYB - but shows a routeing direct OXF^» (Oxford - next trains)>MYB! After a few seconds it removes the list of trains and shows "Sorry, there was a technical error [whatever that means] while searching for your journey. Please try again later".

I presume these are transient issues due to the new file not being loaded yet. The correct super off-peak fare, as rogerw says, is £56.20 for allowed return times, as it is "any permitted route" and both lines are in the routeing guide from Oxford (the routeing point for Evesham) to London Terminals.

Anyone for a bit of simplification?

Fyi, any card will usually start the collection process. Read carefully - if it states that the same card that was used to pay is required, then you have to use that card. But if it doesn’t, any card will start the collection procedure. I have done this when collecting on departure & the card used has expired and also when I forgot to take the payment card with me