I'm sorry, but the knowledge sources provided do not contain any information about the specific error message "RpUser not found" or its cause in the context of Ory or its OAuth2/OpenID Connect flows. The available documentation and issue discussions cover related topics such as session handling, common OAuth2 errors, and troubleshooting login flows, but do not mention this particular error or its resolution. If you continue to encounter this issue, I recommend checking your client and redirect URI configuration, as misconfigurations there are a common source of OAuth2 errors. However, for the "RpUser not found" error specifically, there is no explicit guidance or mention in the provided sources.