One way to fix the_content missing from the Header Footer Plugin for Elementor is going to Settings -> Permalinks and hit ‘Save Changes’ without changing anything.

If you used Elementor Header Footer Builder plugin to build your global header and global footer — https://wordpress.org/plugins/header-footer-elementor/ — but you cannot modify the header nor the footer because Elementor doesn’t load, the first three things before diving deep into debugging are:

1. Go to Elementor -> Settings -> General and make sure the checkbox for “Elementor Header & Footer Builder” is active
2. Go to Elementor -> Settings -> Features and turn on the grid
3. Go to Settings -> Permalinks and hit “Save Changes”