Hi Bestwebsoft,
We are having a similar problem, we have implemented your plugin alongside the following:
https://en-gb.www.ads-software.com/plugins/mailchimp-for-wp/
https://www.ads-software.com/plugins/mc4wp-captcha/
Yet it would seem that any entry into the capcha field is allowed to pass through. You can see this on our development server in the sidebar. The first subscription box is the original embed code. The following is the new form generated by the plugins, as mentioned any capcha input is validated.
You can see this in action here: https://dev-content-desk.pantheon.io/
Any suggestions would be most welcome,
thanks in advance.