Suddenly something that happened last year makes complete sense!
My partner was issued a card by Tomorrow Bank and she used their app to change her pin from the one she was originally provided with.
She then tried to buy something at Boots a few days later, but when she entered her pin the terminal kept saying that it was wrong - she also didn’t know the original pin.
Having separate pins on the network and card explains what happened in this scenario… And yes it was really frustrating not knowing what was wrong or how to fix it so this here makes complete sense: