@guillau
try to edit the file “includes/submission.php” and see if it helps:
wp-content/plugins/contact-form-7/includes/submission.php
delete the elseif statement starting on line 29
elseif ( null != $contact_form ) {
return null;
}
https://plugins.trac.wordpress.org/browser/contact-form-7/branches/4.7/includes/submission.php#L29
Noticed this issue in Firefox browser, while safari and chrome are working fine.
Didn’t investigate in detail but there seems to be an instance of WPCF7_Submission already and this statement returns null instead.
