When sending the page is blank

Hello. A query. I configured Contact Form 7 to send via SMTP with “WP Mail SMTP”.
The drawback is that when testing the form, the emails are sent well, but the page is blank and does not show the message that the submission was successful. Do you know why this can happen?

The blank page is left with this URL:
mydomain.com/#wpcf7-f1912-p1799-o1

CF7: 5.4.2
Wordpress: 5.7.2
PHP: 7.3.29

Thanks.

The page I need help with: [log in to see the link]