Weird, for my scenario I always paid my outstanding balance after cash back redeemed

Statement date: 5th
Redeem cash back: roughly 11th
Payment: between 21~24

Amount as per statement: 1500
Payment amount: 1450

No interest

What was the Statement Due Date ?

The RM50 cashback is treated as payment by SCB

You paid on 7 May but it was not IBFT and was posted on 8th May...thus effectively you are late 1 day.

posting date is more accurate as it is considered "final" state.

just wondering, your ibft from which bank and what time was the transfer?
likely from few possibilities...

1) your bank (where ibft was initiated), coincidentally it was having maintenance down time; any outgoing transfer was processed next day?
2) scb, coincidentally it was having maintenance down time; any incoming transfer was processed next day?
3) paynet, routing or recon issue; hence the delay in posting?
4) or certain bank may have cut-off transfer time, even IBFT <-- havent encounter this
so far, my IBFT from m2u -> scb is same day posting; although i havent tried to IBFT exactly on due date since my payment is grouped with other cc due date which is 1-2 days earlier than scb's.

**just did some digging**

all my payments around end of the month has same-day posting, whereas 1 payment instance in early of the month, has next-day posting -- newly applied card, so the statement/due date is not my choice.

You don't have to pay annual fee or SST to cancel your card if there are no transaction after annual fee and/or SST are charged or posted to your account/card

A couple of guidelines that I use
- don't use cards with annual fee for direct debit (insurance, bills and etc), installment (I don't use at all), or balance transfer.
- stop using the card a couple of weeks before anniversary date (or statement date), and request for annual fee/SST waiver / rebate before using them again, else just cancel the card