So what I gather from what you’re saying is that all the buttons register one input for all 6 button presses?
Joe is right, you have definitely wired up the ground and the signals backwards, however you seem entirely confident that you have done it properly.
Joe is right saying that you have the ground and signals backwards since the logic follows like so
Red is your signal, which is wired individually to each of the face buttons. These lines are all individual and link to one side of the button
Ground is black, which is wired from one point and linked to each and every line. These lines originate from one point and connect to each other and link to the other side of the button.
When this is backwards, you see that all the buttons are individually wired to one ground point, and you have one signal point daisy chained throughout your buttons. This would result in the scenario which you are experiencing.
I never ever trust diagrams anymore because I have bad experiences. Nothing is better than looking at the board and finding out yourself.
you probably knocked the harness loose a bit, open it up and push it back in?