I assume you are using a ios app to connect the DS. As stated in other posts, the ios13 version of the app is unstable. The app does not transfer the wifi settings to DS. Thus DS works from the app only when you are connected to the DS wifi (DS6679 in your case).
Restarting the phone may work sometimes. But i recommend you to setup the DS using a andriod phone. Once set up, it will show up in ios app as well.