The resolution to this is in the following answers post: 
 https://answers.splunk.com/answers/543221/problem-with-saml-cert-error-uisaml-verification-o.html 
 After you add the IdP Certificate Chains (root, intermediate, leaf), go back to Authentication Method page and just click Reload Authentication at the bottom of the page.  Doing this is faster that a splunk restart. 
						
					
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