Getting redirected to the SSO Login page

I have a strange issue where if I hit the base URL (https://<instance>.service-now.com/) after having navigated to the SSO Login URL, I keep getting redirected to the SSO Login page via the auth_redirect.do page. Without visiting the SSO Login URL, I am redirected to the Service Portal (/sp/) page. This is controlled by the SPEntryPage getLoginURL script include. I can confirm I don't have the glide.authenticate.sso.redirect.idp property set to auto-redirect to the SSO Login.

Does anyone know how do I avoid getting redirected to the SSO Login and ensure the URL gets redirected to the Service Portal instead? I suspect the issue might be related to the session cache that gets set once I navigate to a Login page.

Regards,

Ayman