Windows 10 - AAD Device registration failing

Hi,

I am hitting an issue when trying to add a work account to a Windows 10 PC.  The process goes through the normal user name/password prompts then you get the "circle of balls" rotating on the screen and there is stays.  Most users have given up and closed it after about an hour.

I've check AAD and the settings look correct there:

The only odd thing is that the "users may register..." option is greyed out.  I understood this would only happen if the O365 MDM was enabled or Intune (full) was associated with the tenant.  Neither of these products are enabled on the tenant, at least from what I can see they aren't i.e. looking in Azure portal Intune isn't assoicated and if I click on MDM management in the O365 portal it prompts me to set it up.

Just to add to the fun, some users have got devices registered....so I can only assume it did work but something has changed.....

Confused?!

Rob