We have synchronization working with password hash and have been testing seemless sso by going to the website https://myapps.microsoft.com/.com. When I go to that site on a PC that is on the domain and signed in I am prompted to enter my email address. If I do I am prompted to enter my password. I don't believe we should be asked to enter either.
Now the verified domain is set as my primary UPN but is not the default domain suffix, the default domain suffix is a non-routeable .local style domain. So under Seemless single sign on under On Premise Domain Name it shows the non-routeable domain. Maybe this is an issue, I am not sure. As I mentioned my account is configured with the primary UPN of the routable domain and shows correctly under my account in Azure.
This is a new setup and it has never worked.