App-measurement.com DNS blocking causes phone to lose WiFi

Screenshot_20200110_183458_com.ubnt.easyunifi2

A very quick post but one I thought I’d make after my Huawei Mate 20 Pro recently updated and decided that, even though the WiFi was working fine at home, it would frequently fall back to 4G / mobile data. Hopefully this post helps others who’ve been as infuriated as I have been trying to find a root cause to this!

Firstly, some specifications that apply to my particular problem:

  • Phone
    • Mobile Handset – Huawei Mate 20 Pro (O2 SIM)
    • Model – LYA-L09
    • Build – 9.1.0.358
    • EMUI Version – 9.1.0
    • Android Version 9
  • WiFi
    • Ubiquiti Unifi Controller on Ubuntu VM
    • Ubiquiti UAP-AC-Lite
  • Network Firewall & Security
    • Sophos UTM
    • Pi-Hole v4.3 running on Ubuntu VM

My phone would work absolutely fine on WiFi outside the home, but once I got home the device would regularly switch, and stay, on 4G while also still displaying the WiFi indicator in the status bar. The only time I’d really notice was when I tried to fling media across to my Chromecast. The WiFi connection had a strong signal, IP address and could ping anything on the local subnet via the WiFi connection. Anything remote would go via 4G.

 

A quick check on the Pi-hole blocked domains shown “e.crashlytics.com” blocked every minute or so, as well as “app-measurement.com”. I added both to the Pi-hole whitelist and several days later I’ve yet to get any recurrence of the problem so hopefully fixed.

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