Ajax validation not working

I’m building a complex form, and suddenly the Ajax validation has stopped working. I click the submit button, and, if the required fields are complete, it sends the e-mail, but I get no confirmation. If the required fields are empty, nothing happens.

I’ve checked and wpcf7-response-output just keeps having the class wpcf7-display-none when I click the button. I have no javascript errors on my developer tools.

The URL is: https://pmuspicassent.es/es/

Any idea why this isn’t working?

Thank you very much for your time.