your baby bonus may be paid on a different day to your ftb installments
the "one time payment" is totally normal - it is set up as 13 individual payments, not as an ongoing payment
the first payment is around 870 per child, then each subsequent one is 370ish
if your baby bonus hasn't been paid yet (due to be paid monday or tuesday) the next installment won't show on online services as online services will only show you what is to be delivered a max of 14 days into the future.