If the plugin Airplane Mode is installed and active, disregard the settings for use_cdn and assume false (probably would be a good idea to put a filter around that).
Airplane mode is a plugin by Norcross that disables calls to external sites, speeding up local development. Aside from being a popular plugin among developers, it also is now in the popular Desktop Server application
github.com/norcross/airplane-mode