This started happening a few days ago. A user tries to open a link to SPO site or just OWA or office.com and only sees blank page. In case of SPO it tries to open login.microsoftonline.com and never continues. Hitting refresh helps and it actually finishes the sign in process and opens a site. I think this started after we have enabled Seamless single sign on in AD Connect settings and added https://autologon.microsoftazuread-sso.com to trusted sites zone. Previously users had to input their username and password, now it signs in automatically (SSO).
This only happens on Windows 7 PCs and i've been told by support this is because Windows 7 doesn't support Modern authentication. They also suggested to try adding our sharepoint.com site to Trusted or Intranet zone. But then it gets stuck on login.windows.net. They say same should happen when using ADFS (we only use AD Connect now). I guess we will have to postpone SSO until all our PCs are on Windows 10. Which will be only in a few years probably.
Best Response confirmed by
Oleg K (Super Contributor)
Actually, have asked our partners about this and they told us that it should work with Windows 7 and they had clients using Windows 7 that they have deployed SSO for. It could be a matter of some missing update (we only install security and critical). So, MS support was too quick to dismiss this and to advertise Windows 10. Though i feel it can still be tricky to find out what is missing.