About three weeks ago Citi changed the language on the eligibility terms for their credit cards. From a 18 months wait to re-apply, you now need to wait 24 months, in order to get the bonus again. The new rule affected most cards but not all. CitiBusiness AAdvantage card was spared, but apparently not for long.
They are also showing the new language now. You will need to wait 24 months from the time you open or close the previous card.
“Bonus miles and any other special offer not available if you have had a CitiBusiness® / AAdvantage® Platinum Select® World MasterCard® opened or closed in the past 24 months”