The site is: livingquantum.com
Here is the link to the header image: livingquantum.com/wp-content/uploads/2017/02/violetclouds-header-cover.jpg
In Appearance > Header, I do see the proper image selected.
It is NOT a caching issue, as I have now tried it on many computers, several of which have never been to this site, and only the old header is showing. It looks to me like something is malfunctioning in the theme. How can I fix it. And if I can’t, is there another way to get the header to show besides Appearance > Header or as a featured image?