Hello.Please send some screenshots of what you have in: Resolutions and Responsive Design, Template Structure (for mobile), Template Content - Header (for mobile).

Have you tried to upload the entire site?

Robert, assuming the hdr image is in the header itself, check that at lower resolutions the menu is not behind the image. Select image and click icon.

If that doesn't reveal the menu, make sure you haven't hidden it by mistake. If you click on show/hide, then if an object is hidden you can select Hidden object management for each viewport.

However, it is most likely it is simply mostly off the screen to the right.

Once you locate the menu, drag and resize it so it is totally within the available width for the header at each resolution. You should be able to see all 8 handles

As for the image in the header you can resize it for each viewport by dragging the handles or you can perhaps use a different image for each viewport (using show/hide if working in header)

At the moment your header image is roughly twice as wide as the space available on a phone. If you do a preview at mobile resolution

If the header image is placed in the header using template structure, you will need an appropriately sized image for each resolution.