After some days of work, I’ve finally managed to build my app with the native module for background geolocation. I will be definitely writing some article about it soon because it was a nightmare 
Anyway, since I am a lazy person, I don’t like starting up Android Studio everytime I want to develop. Especially considering that native part of the app won’t be changing that often. I am using Microsoft Mobile Center to build it for me. Then I can download APK, install on my device and just run exp start to serve my JS.
This works too, but only if I set DEVELOPMENT_URL in ExponentBuildConstants.java to the tunnel version of the URL the exp gave me. Unfortunately, that’s not good enough as there are other people on the team and it’s nonsense to make a separate build for everyone.
I tried setting the URL to exp700fdde7977948e89f32d3a1b0b02b14://localhost:19000, but that does not work. My device is definitely on the same network and opening http://localhost:19000 in device browser is working fine. Also xde is reporting Sucessfully ran 'adb reverse'. Localhost urls should work on the connected Android device. so it’s strange why it’s not actually working from the app itself.