They stem, in one way or another, from the need to accommodate the addition of journeys to and from Royston on Busway A (as perviously reported). But that has a knock-on effect on Route B times.
In addition, Route A buses that currently terminate at RAF Wyton will now terminate at Hill Rise during the day. RAF Wyton will be served by Route B on Peterborough and Huntingdon rail station journeys. Some peak time A buses will continue to serve RAF Wyton.
There are too many changes to be able to provide meaningful detail here. Fortunately, the new times are available on Traveline (but not - at time of writing - on the Stagecoach website).