Just a thought, but could it be for Sunday's, if the PVR is below 5? (Sorry if it isn't, no clue about most routes south of the Tyne PVR etc wise)
Alternatively, I know that when a bus if off the road at Ashington, when it's fixed, it may return to service on a more local route first, the 35 for example, could it be a similar thing here?
RE: Arriva North East: Latest News & Discussion - April 2015