Header disappearing on all pages after editing and saving

When I want to edit the header of this template and customize it, if I edit the main page, the header is not displayed from the beginning of the editing process. I have to click on the top part to display the header and start customizing the header. Also, I go through the editor and edit the header In both cases, when I customize the header and save it, the header disappears from all pages, but in the edit mode, the header and changes are shown. Only by using clear customization, does the header return to the pages, which means that I have no changes on the header.
Thank you for guiding me