Modern Clix – Header images disappear when viewing posts and pages

I’m using the Modern Clix theme on my blog https://cashdoodle.com

I’ve created a custom header image in the header.php file, and this shows up on the homepage ok, but when I view a single page or a single post, the image placeholders load in, then disappear and are replaced with”home” in text.

I also have the pixopoint navigation plugin running. I tried deactivating this to see if it was causing the problem but nothing changed.