Why does my Wi-Fi Hotspot internet connection sometimes run slow or show that no internet connection is available?
The coverage for the in-vehicle Wi-Fi hotspot depends on the wireless carrier network coverage. When you are in areas where coverage fluctuates, performance may be impacted. In a 2G-coverage area, the Wi-Fi hotspot will not work. In a 3G-coverage area, streaming data or video to your devices may result in the degradation of your service.
See coverage maps at https://www.onstar.com/us/en/services/coveragemaps.html