I presume it's the B and the C? Keep in mind that the keys are essentially pivoted just behind the fall board -- and it looks to me as though maybe the B has shifted the front a bit to the left -- towards the A -- which would swing the back towards the C. And, possibly, stick.
Why? Dunno.
I'm no expert on piano actions! But I can say that you should have a tech. look at it -- do-it-yourself repairs, unless you have a spare piano, can be ... unfortunate. (saying which, he heads off to adjust a couple of dampers... do as I say, not as I do!).