Steps to reproduce the issue

According to documentation, a plugin may interrupt contact form submission by returning an exception onValidateContact. While it does indeed interrupt submission, the user is redirected to the contact form URL, but without any of the contact form components or a meaningful error message.

Here is a sample code snippet that should reproduce this issue:

<?php
defined('_JEXEC') or die;

class plgContactValidation extends JPlugin {

	protected $autoloadLanguage = true;

	function onValidateContact($contact, $data) {
		return new InvalidArgumentException("Exception message is not shown.");
	}
}
?>

Expected result

User should be redirected to the contact form URL, with the form pre-filled with submitted values and the exception message explaining why the submission was rejected.

Actual result

User is redirected to the contact form URL, but without any of the contact form components or a meaningful error message.

System information (as much as possible)

This issue afflicts Joomla! 3.x and 4.x.

Additional comments

I have previously submitted a PR #37540 that resolves this issue by handling an exception onValidateContact the same way com_contact handles failures in its default validation.