When headers are imported into Divi, sometimes characters get added or removed from the Custom CSS Module included in each Header Section.
Here’s an example of what this might look like:

You’ll need to make sure the following values are correctly applied by going into your Theme Builder and then either using the Wireframe view or Layers View to view the Custom CSS Code module included in the section.
Here is a Layers view of Header Section 1:

Notice the “Custom CSS Code for diviwp-header-1” module.
Click on the settings icon for the “Custom CSS Code for diviwp-header-1” to open up the module.
Then search for the following values:
content: "4d";
And make sure it looks like this with a backslash (\) before the 4:
content: "\4d";
Note: there are two instances of this value in the CSS, make sure to update both
Then search for the following values:
content: '33';
And make sure it looks like this with a backslash (\) before the first 3:
content: '\33';
Then search for the following values:
content: '32';
And make sure it looks like this with a backslash (\) before the 3:
content: '\32';
You might find that some values look like this
content: "\\\\33";
Just make sure there is only one backslash (\) and that will fix up the problem.
You’re also welcome to open a support ticket and our support team will do this all for you.