Syntax error in your CSS code
Even a small mistake such as a missing brace can affect all other styles on the page since each CSS rule is located one after another in one file.
The first place which should be checked is the Custom CSS box in the Theme Options. Go to Divi Menu > Theme Options > General Tab at the bottom. Remove all custom code and check if the issue still persist.
Another option is enabling the Safe Mode under Divi Menu > Support Center, the Safe Mode will also disable custom code but only for your account, your website visitors won't see any changes.
Removing all custom code or enabling the Safe Mode and refreshing the page will let us know if the issue related to a syntax error in custom code or not.
If that's the case, the CSS code could should be added back one by one in order to find which code is causing the issue.
The CSS code can be placed in the Advanced settings of the Section, Row or Module. Each piece of code should be checked if custom code was added to the Advanced settings.
Syntax error in your HTML code
Syntax error in HTML code could affect the important part of the page. Some of the important files are loaded in the footer. Incorrect HTML code in the middle of the page could break all tags in the footer.
All custom HTML code on the page should be checked in order to fix the mistake including all modules, and also widgets if the sidebar exist on the page.
Removing all module with custom HTML code and all widgets can quickly identify if the issue related to custom HTML code.
If there is incorrect custom HTML code in your child theme, activating the parent theme will help to identify if the child theme is causing the issue.
Cache
Caching is a very complex set of systems that can easily cause conflicts between scripts. Make sure to always clear all your caches once if changes do not appear on the front end.
Cache may include:
Theme cache:
Cache can be cleared in Divi > Theme Options > Builder > Advanced.
Browser Cache:
(Tutorials on clearing your browser cache)
Plugin Cache:
Usually cache plugin adds own button to the admin tool bar at the very top of the page. If there no such button the cache can be cleared in the settings on the plugin. In some cases the cache is not cleared fully, the cache plugin should be disabled in order to not load cached files at all.
CDN Cache and Server-side Cache:
Depending on what service is used the CDN cache and server-side cache can be cleared in different place or this option won't be available at all, the hostin company may not allow to do this. In both cases the hosting company could do this.