The thing is that contact form 7 is right now not sending the forms that have been submited. I checked this morning deactivating WPML and then, suddenly, the form was succesfully submited. So, somehow, WPML is causing a conflict with Contact Form 7. I'm sharing the debug information with you.
Here is the ticket. I will need to closely examine your website. Therefore, I will require temporary access (WP-Admin and FTP) to a test site where the problem has been replicated, if possible. This will enable me to provide better assistance and determine if any configurations need to be modified.
Please note that it is important to have a backup for security purposes and to prevent any potential data loss. You can use the UpdraftPlus plugin (https://wordpress.org/plugins/updraftplus/) to fulfill your backup requirements.
Your upcoming reply will be treated with confidentiality and will only be visible to you and me.
✙ To resolve the issue, I may need your consent to deactivate and reactivate plugins and the theme, as well as make configuration changes on the site if necessary. This emphasizes the significance of having a backup.
I've been doing some testings and have concluded a few things: the forms have been translated thru WPML Automatic Translations. The only moment when the form works fine is when the WPML plugin is deactivated. Once we activate it, the form stops working.
On Languages > Language URL format, if we disable the "Use directory for default language", the form starts working again on the default language.