Use of the banner landmark

 According to the W3C documentation, the banner landmark (<header>) "typically includes things such as the logo or identity of the site sponsor, and site-specific search tool".

• The elements described above are contained within a <nav> landmark with a label of "Site navigation" instead of <header>.
• Navigation landmarks should only contain groups of links and each should have a meaningful name.
• The type of landmark should not be repeated in the accessible name. The main navigation should be named "Main" instead of "Main Navigation". This is because assistive technology will recognise and read out the type of landmark.
• The page <h1> heading, which is usually the page, course or module heading, is contained in a <header> landmark. The use of this landmark in this context may not be appropriate.

This could be a failure of Level A WCAG 1.3.3 Info and Relationships.