I wonder if this is because GF is overseas and effectively their bank are sitting on the payment (interest, thanks very much!)? Equiniti Paymaster pays Armed Forces pensions for veterans living overseas on the date they are due. Payments are then routed to overseas bank accounts via Citibank. So they, or a bank down the line may be changing the payment date whilst holding the money owed? Or, maybe it’s the delay of transfer that has effectively moved the dates?
My pension gets paid on 10th of the month. Not sure I would want to delay it by 20 days to give Equiniti another 20 days of interest. Better off in my account earning interest than theirs!