This used to be a common problem with Czech Unicredit M&M credit card. Apparently the credit card prolongs the miles in the background until end of (next) quarter, and awaits to see further mileage credit (as a proof card is being used) to prolong it again. Sometimes card issuer would send the information late, or something would happen on M&M side, and the validity would be revealed to the user as if they stopped using the card.