I said I would post back on experience.
I had 3 Citi cards with the Circle K Gas 10% offer, up to $5.00, may use offer 2 times
That means 6 opportunities to get cash back.

I'm amazed but 5 out of 6 of those transactions resulted in cash back.
But 1 out of 6 did not. No rhyme or reason.
I controlled myself (or tried) at least to not contact Citi for the last credit but I tried chat and as everyone would guess was told..."I'm sure it will post."
Mind you it's been 30 days since transaction and were one statement post date. All other credits posted in 5 business days.
The agent then said "it's called a statement credit because they post on the next statement." Umm okie dokie.
I'm letting it go as I'm just thankful that I got 5 out of 6 to work - but the inconsistency by far removes any confidence in the program and I probably wont use it in the future unless I know I wont get worked up if I dont get it credited.