Hello,
Most likely it happens because of the incorrect implementation of CAPTCHA. Unfortunately, we cannot say exactly where to insert the code, since there are many different custom forms and the code should be inserted individually to each of them. Also, we see script errors on your page. If you want, we can help you with this issue, however this is a paid service, since we need time to study your form and implement CAPTCHA to it. If you agree, please create a private ticket on our support forum https://support.bestwebsoft.com/, and provide the link to this post, so that we`d understand what are you talking about.
Regards,
BestWebSoft Support Team