I see this question from time to time in the Divi Facebook groups, so I wanted to address it publicly. There actually is not an issue, and it is not a bug. Once you hear the explanation, it will make sense.
The issue where the Divi Email Optin module is not shown happens when you do not connect an email providers. Without an email provider, there is not way to know what form fields are needed, and certainly no need for a form. So the solution is rather simple. Just connect the form to your account, such as Mailchimp, and the form will show up on the frontend!