Make sure that you don't have any third-party comments plugin installed. If you have one, please deactivate it and check Captcha.
If the problem remains, try activating a standard WordPress theme for a while (Twenty Twenty, Twenty Nineteen) and check the results.
If the problem still remains, please submit a request, and provide a link to the page where the problem occurs.
This article related to Captcha by BestWebSoft plugin
Additional resources: Captcha - User Guide
Still need help? Feel free to contact our friendly support team. Create a private ticket