Thank you so much for using our theme SuperMagPro. SuperMagPro is a magazine theme and we imagined that each post contains feature image. So, when a post doesn’t have any featured image a default image will appear there. So we recommend you to use the featured image for every post or set the default image from customizer. It will be best for you.
Go to Appearance > Customizer > Extra Options > Custom No Images.
Please try once and if not solved, let us know.