IdP-Initiated login is not enabled for connection error when SP-Initiated flow configured

We have IdP-Initiated logins disabled on purpose so getting the error is fine. The problem we are trying to solve is why we are getting the error in the first place.

We are configured with an SP-Initiated flow and Auth0 documentation says we can get the “IdP-Initiated login is not enabled for connection” error when in SP-Initiated flow if 1) the RelayState is missing or empty or 2) the InResponseTo attribute in the SAML Response is missing or empty.

I checked the Auth0 log entry and see both the RelayState and the InResponseTo attribute in the SAML Response. Neither are missing or empty, so the SP-Initiated flow should be fine.

Does anyone know why an SP-Initiated flow with both RelayState and InResponseTo attributes set, would cause the “IdP-Initiated login is not enabled” warning?