Welcome to the Auth0 Community 
I did a response on another post here about SAML responses which may help you as you can normally capture the SAML response in the browser dev tools.
On your side note, as far as I know if the SAML request is accompanied with a RelayState and the SAML request contains an ID attribute then I would expect the SAML response to also be accompanied with a RelayState and also include an InResponseTo which matches the ID attribute in the request.
Hope that makes sense.
Warm regards.