APM session expired message customization not showing after policy timeout

For an SP SAML initiated setup using F5 as the IDP and using the F5 logon page, when the session timeout expires we want to customize the built-in session expiry message including a link to start a new session. When this expiry occurs APM removes the session and with that all variables. The problem occurs when clicking the "open a new session link" this will create a new session directly to the IDP, hence is not able to process SAML because simply it did not receive a proper SAML request.

In my opinion the best solution would be to redirect is back to the external SP, but this would be technically impossible because all APM related variables are gone. I know the expiry timeout is generated by an built-in Java hard-coded process.

To workaround this I tried to customize the APM session expiry message more specifically here in general customization text menu:

APM policy >> access policy >> ending pages >> deny >> general >> session expired message

The issue is that the new page is not loading properly it does not show the customization.

So to summarize we have actually to issues here:

1 when policy timeout expires the APM session is closed and we are unable to redirect to external SP website (which would be more user friendly)

2 the customized session expired message is not showing after saving and applied policy

Perhaps someone here want to share there knowledge on this particular integration issue.

Thanks