An error "invalid bearer token received" may be received while attempting to authenticate with SAML, preventing a user from authenticating successfully.
A workflow can be published to a lower Server version if the Gallery information also exists in the machine. Manual running of the workflow will throw out "Problem Loading App" but a scheduled job will run without an error. The most you see is a warning in the engine log.
Attempting to publish workflow from a higher Designer version to a lower Server version displays incorrect error or a blank window. If there are existing Gallery details, the workflow can be published.