For some reason, I am only getting a signal for xPin (packet[0]) and packet[1] does not move...

reciever.ino

#include <TimerOne.h>

const byte xPin = 9;
const byte yPin = 10;
const byte ledPin = 3;
const byte period = 32; // for 8 bit DAC 

unsigned char packet[3];

void setup(void) 
{ 
  pinMode(xPin, OUTPUT);
  pinMode(yPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  Timer1.initialize(period);
  Timer1.pwm(xPin, 512);
  Timer1.pwm(yPin, 512);
  Serial.begin(9600);
}
 
void loop(void) 
{ 
  analogWrite(ledPin, packet[2]);
  Timer1.setPwmDuty(xPin, 4*packet[0]);
  Timer1.setPwmDuty(yPin, 4*packet[1]);
  delay(1);
}

void serialEvent() {
  if(Serial.available()){
    unsigned int thisByte = Serial.read();
    if(thisByte == 255) {
      Serial.readBytes((char*)packet,3);
    }
  }
}

sender.cpp

#include "testApp.h"

void testApp::setup(){
    ofSetWindowShape(900, 600);
    serial.setup("/dev/cu.usbmodem1431", 9600);
}

void testApp::update(){
    unsigned char x = ofClamp(255 * mouseX/ofGetWidth(),0,254);
    unsigned char y = ofClamp(255 * mouseY/ofGetHeight(),0,254);
    unsigned char message[4] = {255,x,y,ledVal};
    serial.writeBytes(message, 4);
}

void testApp::draw(){
    ofSetColor(ledVal,0,0);
    ofCircle(mouseX,mouseY,10);
}

void testApp::mouseMoved(int x, int y ){
    mouseX = x;
    mouseY = y;
}

void testApp::mouseDragged(int x, int y, int button){
    mouseX = x;
    mouseY = y;
}

void testApp::mousePressed(int x, int y, int button){
    ledVal = 255;
}

void testApp::mouseReleased(int x, int y, int button){
    ledVal = 0;
}

sender.h

#pragma once

#include "ofMain.h"

class testApp : public ofBaseApp{

	public:
		void setup();
		void update();
		void draw();

		void keyPressed(int key);
		void mouseMoved(int x, int y );
		void mouseDragged(int x, int y, int button);
		void mousePressed(int x, int y, int button);
		void mouseReleased(int x, int y, int button);

        ofSerial serial;
        float mouseX, mouseY;
        unsigned char ledVal;
};