I use Yoast with Divi on the latest versions of WordPress, Divi and Yoast. Sitemap works 100% for me here is my sitemap https://georgenicolaou.me/sitemap_index.xml

A few things you can do in order is

1. Go to your WordPress Dashboard
2. Find SEO on the left. Click on the Features Tab
3. Look for the “Advanced settings pages” option Make sure it is enabled
4. Now again on the left where you found SEO there should be one under SEO called XML Sitemaps
5. When you are there it says Your XML Sitemap You can find your XML Sitemap here: XML Sitemap
6. Click on the link XML Sitemap the link should take you to http://www.whateveryourdomainis.com/sitemap_index.xml
7. If it says 404 page not found then go to your Dashboard–>Settings–>Permalinks and select the option that says post name and click save. If you already have it selected just click save
8. Do steps 4-6 again.