Terms and Condition accept checkbox is not responsive

At signing up a new user, the Terms and Conditions field has an Accept checkbox that is required. When clicking on it first time it doesn't change and after clicking the second time it displays a warning: * This field is required.
I don't know what parameter in the Terms and Condition field is controlling this behavior or if it is controlled from somewhere else, e.g. global settings.
If I make this field Not Required, I can proceed with the registration but I need it to be required.

Please advise.

It's just a plain ol' HTML checkbox input. So that shouldn't be happening unless you've some sort of JavaScript on your site acting on click events for it. Edit your terms and conditions field in CB > Field Management and provide what you've configured under Parameters > Display. Under Integrations be sure you're not using any integration validations on it as it doesn't particularly need any additional validation behavior. Please also provide what Joomla version you're on.