Next button hangs on checkout and when clicked throw an error

The "Next Button" on the checkout page hangs and an error is thrown once clicked. As of right now the next button is being hidden with CSS, and can be found in the customizer > additional css:
.mp_checkout_section_content .mp_checkout_buttons {
display: none;

This button is throwing an error when clicked and it hangs:

validationTargetFor 'validationTargetFor' is undefined