$mail = new PHPMailer(true); statement is failing

Question

I am troubleshooting a code I inherited, and code that includes PHPMailer stopped working earlier this week. Here is a stripped-down code version with echo statements inserted to see where it fails.

<?php

echo '<p>First Debug line<br></p>';

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;

echo '<p>after use<br></p>';

require 'vendor/autoload.php';

echo '<p>after vendor/autoload.php<br></p>';

$mail = new PHPMailer(true);

echo '<p>After PHPMailer<br></p>'; // this statement does not get executred

REV 1. Added following error trapping and I get the following now. What is puzzling to me that it was working a couple of days ago...

First Debug line

after use

after vendor/autoload.php

Fatal error: Uncaught Error: Class 'PHPMailer\PHPMailer\PHPMailer' not found in...

<?php

ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');
error_reporting(E_ALL);

echo '<p>First Debug line<br></p>';

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;

echo '<p>after use<br></p>';

require 'vendor/autoload.php';

echo '<p>after vendor/autoload.php<br></p>';

$mail = new PHPMailer(true);

echo '<p>After PHPMailer<br></p>';