Ebucks monthly Kauai voucher

FNB’s Ebucks rewards programme allocates a monthly Kauai voucher to their members. This voucher is valid for one month. During April it wasn’t possible to use the voucher earned from March rewards and now, after the April awards have been allocated the March voucher is “gone”. Under normal circumstances I would have used my voucher and would not have forfeit it. Why did Ebucks decide to cancel vouchers earned when we could not use the voucher?