I suspect there is a bridge on the other side of the PCB where I've drawn a dotted red line here:
That would put all 3 switches in the same line, and there might be a break where I've drawn the circle.
I don't think there is static damage to the IC, or more than 3 keys would be affected.
Do you have a multimeter? Using one to check that there is an electrical connection where there should be would help isolate the problem quickly. Buy a cheap one if you have to, you don't need anything fancy, just one that measures resistance.