OJS 3.3.0-15 Suggested Reviewers Plugin prevents sending emails

I have an email setup that sends messages. But after I added the Suggested Reviewers Plugin to Open Journal Systems, I had problems sending messages. In the logs they write this:

AH01215: PHP Warning: Undefined property: MailTemplate::$submission in …/plugins/generic/suggestedReviewers/SuggestedReviewersPlugin.inc.php on line 318: /var/www/usr/data/php-bin/…/php, referer: https://…/index.php/…/management/settings/access

There is a function in SuggestedReviewersPlugin.inc.php:

public function sendMail($hookName, $args) {
        $form = &$args[0];
        $submission = $form->submission;
        if ($submission) {
            $publication  = $submission->getCurrentPublication();
            $excludedReviewers = $publication->getLocalizedData('excludedReviewers');
            $recommendedReviewers = $publication->getLocalizedData('recommendedReviewers');
            $args[0]->privateParams['{$excludedReviewers}'] = htmlspecialchars($excludedReviewers);
            $args[0]->privateParams['{$recommendedReviewers}'] = htmlspecialchars($recommendedReviewers);

Line 318:

$submission = $form->submission;

However, the emails that I send with the plugin enabled only arrive when I disable the plugin. Any messages, not only those related to the publication of the article, but also those messages that I send to “Users and Roles” are not received.