Problem:
When translating a page, it includes content that doesn't exist on the page. Upon investigation, I found that this is content that was added to the native WordPress editor. Upon switching the editor to Divi Builder, it saves it in the background, so it can be restored when you disable the Divi Builder again.
The problem is that WPML also sends this old content to the translator, who will then translate and charge for it. I can't find a way to get rid of it from within WordPress/Divi, so was hoping there is a way to exclude it from being send to the translator.
Solution:
The field that you're looking for is _et_pb_old_content.
I'm not sure if this field is needed by the Divi builder or not, but I went to WPML → Settings → Custom field translation, searched for this field, pressed the lock icon to be able to change its settings, and set it to copy (just to be safe).
Now, I went back to the page I created (in the original language), just hit the Update button (without opening the page in Divi builder), then updated the translation. This time, the field-_et_pb_old_content didn't appear anymore.
Relevant Documentation:
https://wpml.org/documentation/getting-started-guide/translating-custom-fields/