Using New Outlook on Windows for personal email, calendar, and contact management
Hello Thomas Heffernan,
Good day! Thank for your reply and sharing more useful information!
For my suggestion, please try all of my workaround step by step to fix your issue. If this case still persists, you may have to contact New Outlook for Windows Support Team via clicking Help>Contact Support or Contact support and provide feedback within the new Outlook for Windows. Please do not mind that we could not provide further assistance because need to check from backend side and we appreciate your efforts in this case. The support team over there has higher permission than us, they can remotely help you and collect logs at your convenience. They can also involve more resources to investigate the issue from backend side.
Again, your understanding and patience will be appreciated.
Thank you!