There is some question as to whether it's even particularly useful to have the charger on the internet at all. These are not complicated devices, and you can always wait for a needed firmware update before connecting it. I didn't bother, personally. It delivers 48A to the car, so it works.
Turn on airplane mode, then turn on wifi only. I imagine that your phone is deciding it would rather connect to the cellular based data(and its full internet connectivity) than your HPWC with ZERO internet connectivity. It might also help to turn off your home wifi or otherwise tell your phone not to go finding a different wifi access point(via autoconnect)