But of course, OP only applied for 2 cards from Chase, and even at that, one was personal and one was business. The last previous app was 9 months ago, so no problem there.

The word lately is that Chase is getting much more difficult to get bus apps approved than it used to be. Hopefully you have been doing some regular spend on that United card, since unlike Citi Chase takes notice if you've been spending on the cards you already have when you apply for more.

In any case, you should call the Bus Recon line, and talk with them. It's easier to talk someone into approving an app than it is to talk them into overturning a denial once it happens.