IdP HTTP-POST binding stucks at SP's bindingTemplate page

[William Lee]

Hello,
We use both Shibboleth SP and IdP, after SP sets to HTTP POST SAML binding for outbound SSO requests (default is HTTP Redirect binding), initial redirect to IdP login works fine (it does briefly display SP's bindingTemplate.html page), but after session timed out, supposed to redirect to IdP to renew session, browser page stucks at SP's bindingTemplate.html page:
You are automatically being redirected to the authentication service. If the browser appears to be hung up after 15-20 seconds, try reloading the page before contacting the technical support staff in charge of the authentication service you are trying to access.

Redirecting...

I'm wondering what could have caused this?
Thank you!William
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