What all was done to the controller? What all was tried? No one knows if it was brand new out of the box like that, or it it's had 15 people that don't know one end of a Resistor from the other put their fingers all over it.
If it was messed with, even by one person, especially if they were adding duplicate buttons, then it could be anything, though I'd suspect the X line is shorted to ground wherever they were messing around.
If it's a pretty much untouched controller, then the Cap on the X line is what I'd remove first to make sure that thing isn't shorted or dragging down the line causing it. Then if that doesn't do it and there is no obvious signs of a short on that X line then the PCB could have a manufacturing error as that X trace is buried in an internal layer or the MCU is suspect as all button lines pretty much just go go right to it.
