Sending same submission twice

What other plugins and theme do you use on the site?

The theme is custom built.

Advanced Custom Fields PRO
Better Admin Bar
Better Search Replace
Cache Enabler – I read it could be cache so disabled this!!!
Contact Form 7 Captcha Pro
Custom Post Type UI
EventON
Fancy Admin UI
GDPR Cookie Consent
iThemes Security
Nested Pages
Yoast SEO

Try switching to the default theme and deactivating all plugins excluding Contact Form 7 and Yoast SEO.

Why you are advised to deactivate plugins and switch to the default theme.

Hello,
I’ve been trying for a few months to find a solution to this problem that seems to be chronic and I’ve found complaints of the problem that are over a year old.
I manage several sites with contact form 7 and they are all having the same problem of sending with duplicity with a difference of seconds between one and the other.
Today I created a new wordpress installation and installed and configured contact form 7 for a new website and it had the same problem.
It seems evident that it is a problem with the Contact Form 7 plugin, regardless of what is installed along with it.
I hope there is a solution to the problem, because although it is an excellent plugin, we will have to look for other solutions if there is no solution.

Here are some of the many related and unresolved topics.:
https://www.ads-software.com/support/topic/duplicate-entries-and-emails-after-submitting-contact-form-7/
https://www.ads-software.com/support/topic/contact-form-7-sending-multiple-emails/
https://www.ads-software.com/support/topic/duplicate-emails-sent-3/