I am using JIRA or Confluence. I changed my Base URL from JIRA/Confluence, but in every new SAML Single Sign On Process, the SAML Request still has the old Base URL.
The SAML Single Sign On Plugin does not notice himself, if the Base URL changed. So he attach the old Base URL in the SAML Request. In this case you need to "Save" the Plugin Configurations again, even if you make no changes in the configurations. You also can disable and enable the plugin, which has the same effect.