Your issue is that you have is related to your custom code, by that I mean you have set the BrandNav into the Sidebar. The BrandNav by default doesn't support the Sidebar area.
Please be aware that we do not provide support to user created code nor do we provide support to users who have created child sections of core sections, as this too is considered user created code.
If your customized BrandNav is having an issue on the Contact pages only, then I would probably say its related to the Contact form. Try removing the form from the page and see if the menu appears in the correct location. If it does, then its form related and you may need to adjust the CSS or try another form plugin.