StorageService-backed RelayState mechanism did not return a state value.

[Cantor, Scott]

Also, to be clear, the reason I interpreted your original description of the problem as a RelayState break was simply that you explicitly said it was logging an error that indicated it wasn't reading back the state token, and the usual result of that is a redirect to the root of the server after it logs in. Often that's not protected, so the appearance is that you're not logged in (e.g. the Apache log showing the user identity missing) even though you are.

I've never heard of RelayState tracked in memory going missing for any reason other than a node switch or an extended time elapsing between AuthnRequest and Response (or shibd restarting I guess). If something else can cause it, that's news to me. It would require a manipulation of the form from the IdP or with the POST to the SP literally corrupting or dropping the form field.

-- Scott