In short:
On 9th April, there was engineering work in the Hambleton Jn area all day, meaning that Anglo-Scottish trains were reduced to one an hour from London and diverted via Askern (where there are only a certain number of paths available, and rolling stock constraints also need to be considered, as the route is not electrified).
The second train each hour to Edinburgh generally started from and terminated at York as a result.
As Leeds services were able (in infrastructure terms) to run as booked, these were broadly unaffected, except where there were a small number of changes as a consequence of the engineering above.
On such change was that the 0615 departure from Kings Cross, which on a Saturday usually runs to Edinburgh, was planned to be diverted to Leeds, serving all stops up to and including Doncaster as booked.
Other than noting that this service wouldn't normally call at Wakefield in any case, I don't want to get into the whys and wherefores of adding a call there on this date - however I hope this provides a brief background as to the reason for the planned service alterations on that date
