Coupon box creating random code display in email customizer

I am using the latest woocommerce and do not have any customization. I am also using the premium version of coupon box. When I go to the default woocommerce email customizer, there is some coupon code html code displayed below email template (see attached screenshot) – when i disable coupon box plugin, the random code goes away.. i think coupon box is the issue.. please check