How long are the wires from the piezo disk to the piezo PCB? I can't see where you have the board mounted.
You also need to include a delay into the probe routine ( include R0.5 in your M558). This makes the printer wait for half a second between XY movements and Z probe movments to allow vibration to die down. Also, you should probably use the P8 mode rather than the P1, the output of the piezo PCB is digital, using P1 (analogue) only increases the chances of false triggers.