This KB talks about a scenario where we have built a custom portal with the login page as the landing containing few custom widgets. When we try to access the portal page, for example, https://<instance name.service-now.com/<portal> all the users irrespective of their roles are redirected to the platform UI page instead of the custom portal page.
The scenario has SSO enabled on the instance. After activating the browser developer tools and collecting the traces from the Network tab when accessing the portal, we could see the auth_redirect code doesn't carry the portal page in the relaystate of the SAML request URL
The relaystate points to navpage.do when redirected to the identity provider for authentication. Just before these redirect calls in the browser traces, we could see few calls to https://<<instance name.service-now.com> which is the cause for the loss of portal page in the RelayState parameter of the URL during the redirection.
The cause of these calls is due to the duplicate custom widgets added to the landing page mapped to the portal record
Deleting the duplicate and unwanted widgets which are pointing to the instance page from the login page mapped to the custom portal record will allow for the right construction of the RelayState with the portal page during the redirection in the SAML request.