Header image only showing black box

Hi, Hopiong you might be able to help. I've added a header image, however it's very hit and miss whether it actually displays this in the preview. Sometimes I have to keep re-adding to get it to show. However once published, when checking my actual site I only see a large black box. Sometimes pressing F5 will get the image to show briefly before it vanishes and turns back into the black box. Got it set to Homepage/Front Page - shorturl.at/jAMN5 Any help greatly appreciated.