The issue is ( could be, I am not the dev ) that whenever Contact Form 7 generates the form shortcode it doesn’t create a name attribute and it doesn’t seem to fallback to using the title attribute of the shortcode.
HTML5 doesn’t like empty name attributes, this is an issue on WPCF7 side IMO. One solution ( for the dev ) could be in the wpcf7_contact_form_tag_func() ( /includes/contact-form.php Line 880 ) function to check if html_name attribute is empty, and if it is, generate the title attribute as the name.
For Users – A short-term solution until this is fixed could be to add an attribute to your Contact Form 7 shortcode html_name and give it some kind of string value. This will solve the validation issue. It’s something WPCF7 should handle but it works in the meantime.
E.G. [contact-form-7 id="4" title="Contact Form" html_name="Contact Form 1"]
