According to Mark Hopwood yesterday at Travelwatch Southwest, further cuts are being made to the Summer Sunday timetable at the May timetable change, as part of the management of this problem.
........as part of the
failure of management of this problem - fixed it for you!

I have some disquiet over service reductions though
in certain instances they can make sense.
At Melksham, we lost two round trips on Saturdays "so that the others can be more reliable". The services lost were the ones that had been running pre-2013 and we were left with just the Westbury - Swindon shuttle with extended gaps in the middle of the day where those previous skeleton services had run. In some ways a logical cut, as the trains cut had been run at times the stock wasn't really needed on other lines either - quietest time of day. However, I spite of us being told they were being cut to help reliability, the reliability of the remaining service got worse.
This broke the promised message we had been sold - "fewer trains but more reliable" though of course we don't know if it would have been even less reliable had they remained.
As a result of this failure to deliver what we were sold on, we find it harder to trust GWR▸ these days.GWR services on the South Coast to the east of Portsmouth - to Brighton - were also lost. Two round trips a day. There was sadness rather than retention campaigning as they were lost. Again, comment / promised that it will "let us do better / be more reliable with the other services" which has had a hollow ring, and I'm not sure that the promises - or implicit promise of the marketing hype - has been delivered.
In December, GWR cut a peak train from Warminster to Westbury in the interest of "the reliability / time keeping of other busier trains". Problem is that as a result, they then offered no route home for students and working people from Salisbury from 16:42 to 19:13 - for sure, there are fewer passengers on the train culled than on the one it held up, but should they really be prioritising saving a couple of minutes delay over getting people home at all? With an extra call on the train that was got in the way of sometimes, the issues could have been compensated. But, no, in spite of their being three minutes of extra allowances in that train, they won't add the call and seem to be intent on performance stats one serving their existing customer base. And - we were presented with a "fait accompli" on this one - no notice at all of the significant change prior to it happening and the train just disappearing from the timetable.
So - whilst we appreciate the need to update timetables, and to provide a reasonable level of service overall that may be a lessening for some, we treat planned cuts with extreme unease and we don't trust (sorry) GWR to deliver the benefits to us that they promise.