This blank page is caused by a delay during form submission. For example:

• The Identity Provider (IdP) is taking time to authenticate.
• The Service Provider (SP) is processing the Security Assertion Markup Language (SAML) response.
• There are network delays between the browser, IdP, and application.

Because of this, Mendix has no control over what the browser displays during that period. The browser is waiting for the next page response. For context, a message such as Signing you in... could be shown only if the delay were to happen on the Hypertext Transfer Protocol (HTTP) POST auto-submit page generated during SSO.

As such, this behavior is expected.