Using New Outlook on Windows for personal email, calendar, and contact management
The best thing to do is to submit an In App ticket for this issue via Help, Support. When you submit the ticket include this forum thread, so the engineers see this is affecting multiple users.
If you use Outlook Web Access (OWA) are you able to add the contact from there, https://outlook.office.com/mail/?
I'm following up with escalation engineers to see if they have any other guidance about this issue. I'll post back any guidance I get.