Case mismatch in PHPMailerException namespace declaration

Whenever there is an error in PHPMailer, it does a:

throw new phpmailerException

However, the namespace is declared as:

use Drupal\smtp\Plugin\Exception\PHPMailerException;

With different casing which causes a RuntimeException instead:

RuntimeException: Case mismatch between loaded and declared class names: Drupal\smtp\Plugin\Exception\PHPMailerException vs Drupal\smtp\Plugin\Exception\phpmailerException in Symfony\Component\Debug\DebugClassLoader->loadClass() (line 198 of /app/vendor/symfony/debug/DebugClassLoader.php).

This was observed in PHP 7.1, Drupal Core 8.3.5