I ran into an issue and I don't think I've seen it logged here. When I run through the wizard, if OneDrive already has someone defined in the secondary admins either via SharePoint User Profiles management or PowerShell, it lists the change option but it's not a link or button and you can't do anything with it. You have to go to SharePoint User profiles piece and change it there and then it will allow you to do it.
I did find that if you use the wizard to set someone, go back and then it will allow to use the change button.
Second issue, I've had a few occasions so far where the wizard has not created the shared mailbox. I've had to go in, give it a license again and use the convert in the exchange admin center and then remove the license.