It is not wired like the diagram or it would work. Only you can see how it is wired.
If you post some pictures of the switches maybe we can see the problem.
The one possible thing is you wired by the position of the wires in the diagram. You can't always do that. The screws are not always in the same position. Look at the colour of the screws on the four way.
If you post some pictures of the switches maybe we can see the problem.
The one possible thing is you wired by the position of the wires in the diagram. You can't always do that. The screws are not always in the same position. Look at the colour of the screws on the four way.