ANSWER:
When updating from a single IDP SAML version to multiple IDP SAML version, please note your metadata file location changes. This means your IDP needs to change the SP Metadata URL specific to the alias name.
If not changed it will point to http://<Application Root URL>/SSO/metadata/
and will not get the encryption information specific for your configuration.
The SP metadata for your app can be obtained by clicking Download SP Metadata on the final configuration step to download the XML file or by opening http://<Application Root URL>/SSO/metadata/<IDP-Alias>
for your app’s URL.