Starting with version 4.2.3, we have changed the functionality for faster and more correct plugin work.
You need to replace the output and response checking for the CAPTCHA in your form according to the instruction or the appropriate point in the FAQ (see "I would like to add Captcha to the custom form on my website. How can I do this?").
After making changes, simply close the message in the admin panel. If you completely updated the CAPTCHA interaction with your form the message will not be displayed any more.