Hi Jonathan,
Thanks for your feedback. I totally know about your concern. As we’re not masters of local AD, and we lack detailed information about AD configuration. I am so sorry that we cannot provide further instructions on my side. Your understanding is highly appreciated.
If our community members have related experience on this scenario, I will appreciate it if they can share some information here.
Moreover, some community members have raised the same issue before, such as the thread I mentioned above, and we also suggest them post this issue in the Technet forum for a better response. To get more detailed information about this deployment, you can also try to post this issue at the Technet forum. Maybe their community members have related experience on this issue.
Jonathan, thanks for your understanding, enthusiasm and working closely with Office 365.
Best regards,
Young