"One Page Express" theme's Front Page should only be modified using the Appearance --> Customize.
If you have used Elementor to modify the Front Page and saved the page, you will notice:
Symptom 1 : the header will overlap the first section at the top of the Page, like the following screenshot:
Symptom 2 : When you go to Appearance --> Customize, the "manage page sections" will be empty even if sections are in the Front Page.
If you are experiencing this problem, please revert to an earlier revision of the Front Page.
How to do it:
1. Go to All Pages --> look up "Front Page".
2. Click on Edit.
3. On the right hand side, in the "Publish" section, find "Revisions".
4. Click on Browse.
5. In the next screen, choose the last saved version of the page.
6. Click on "Restore This Revision".
7. Check the Website's Front Page to make sure it has returned to normal.
Tip : You can also use Revision to undo changes made to your other Pages or Posts.