Hi,
It's now showing a plain gray header on every pages except the "Job List" page, you can't see the problem because I hidden those pages title to temporary avoid this problem showing to the public.
I simulated the problem at the following link for you:
https://ukcareer.co.uk/sample-page/
Please use the admin account to the page, then change the site layout to Fullwidth, you can see the header image immediately, and the image become a gray colour box again if you change the it back to a boxed design.
Thanks for you follow up actions, hope it could be fixed soon.