Signed up to do this post, and I do realize it was started over a year ago. But I thought I would mention what my fix was for this issue. After trying options from others my situation was different, it was working fine over LTE. In the app you have the Internal URL and you have the External URL in the application. I noticed my IP was a 10.10.1.1/24. The app was looking for the Home Assistance instance, on the wrong network. Removed the Internal URL and that fixed the issue.
You could also just add the SSID for the network, so if the IP’s match it will know to look at the SSID.
Hope this helps!