Well, just because you were reissued new tickets for a different flight, that different was still paid for with your AA Citi card. So whichever it works, it was because it lost track of your card-based status (whether that's due having a card or due to using the card) with the ticket reissue. If AA hasn't yet established this new level of status (Silver? Tin?) completely within its system, it may not have the ability to carry it over in such situations the way Gold/Plat/EXP status carries over in rebooking situations.
The reason I suspect it's tied to having the card, not to using the card, is because multiple people who have the card have recently booked tickets with Avios points they had, then changed the ticket to be associated with their AA number rather than their BA number, and got priority boarding. (A similar procedure has long worked for Gold/Plat/EXP members; book a ticket on AA with a partner airlines' miles, then change the account the ticket is linked to back to AA, and they have their Gold/Plat/EXP at-airport benefits on that ticket.)
Plus, in the very first post of this thread, there's a link to a page that links to this page:
https://creditcards.citi.com/credit-...m-information/
where it says, in part:
First checked bag freeFor benefit to apply, at the time of booking, Citi® / AAdvantage® account must have been open at least 7 days and reservation must include the primary cardmember's American Airlines AAdvantage® number. This benefit is valid for travel booked and ticketed on or after April 2, 2012.
As you can see, it doesn't say anywhere that the ticket has to booked with the card, but how long the card had to be open, when the ticket had to booked after, and that the cardholder's AA number must be on the ticket (by the time you're checking your bag).
It then goes on to say extremely similar things about the priority boarding.