The Divi theme includes a feature for creating page templates with custom headers, footer and / or layouts, known as the Divi theme builder. If you are trying to disable a custom header built using the Divi theme builder, but are unable to restore the default Divi header, here's a possible explanation
The Theme Builder is Disabled, but not Deleted
You might notice that, in addition to the default Divi header not displaying, the Header and Navigation theme customizer section is missing. This customizer section only applies to the default Divi header and is hidden by Divi when a custom theme builder header is used.
The missing default header / customizer options problem can occur if you disable the theme builder header within the customizer, like so:

To restore the default header you need to actually delete the header from the theme builder (i.e. using the "trash can" icon shown in the screenshot above). If you want to keep your header for future use you can save it to the library before deleting. Once deleted, the default Divi header should be restored and the customizer options should be back.
I did as this article suggested, but the default header and the option for it in the customizer is still gone! Any ideas?
Hi Laura, I'm not quite sure… if you're willing to share login details via the contact form I'll be happy to login and take a look to see if I can spot the issue. Thanks!
Thanks Dan. This helped me go back and restore the default navigation settings before going forward with the theme builder header. I was hoping it would fix the jumping header. It didn't, but it's nice to know the default nav isn't gone forever!
Hey Janice, I'm glad that helped restore the settings. I wouldn't expect it to solve the jumping header issue. There are some tutorials out there on how to fix it by setting the page container padding in CSS, e.g.:
https://www.markhendriksen.com/how-to-fix-divi-jumping-header/
If it doesn't help, please feel free to send through a link to an example page and I'll try my best to help with it. Thanks!
I have tried everything, watched numerous youtube videos, but this article solved my problem. My header disappeared from many pages on my site and the Header and Navigation setting was missing too, but this post helped me resolve it as I was only hiding my custom header in divi theme builder. deleting it and making my header module visible solved it. Thank you!
You’re welcome, Dami! Pleased to hear it :)