Ads "Facebook Audience Network" not being blocked

3 apps:

a) Web View which is used by an RSS app I use (this is based on the native browser)
b) Native Android Browser "Android_external_chromium-webview"
c) Icecat

Using AdAway with the default hosts file

I keep getting lots of ads from "Facebook Audience Network" when using either a) and b) but NOT c)

This would seem to indicate that Icecat is working properly and the /etc/hosts is doing its intended job.
OTOH, a) and b) continue to show these ads (I can tell where they come from since there is a small "Facebook Audience Network" tag which one can click on, at upper right corner of ad frame) but that .Android_external_chromium-webview is bypassing the hosts file possibly by going via a proxy (or something).

I do NOT have or see a setting for "Data Saver" or "Data Compression" under "Settings": for this browser, nor do I have "Data Saver": enabled under the General Android settings (which I believe is not related anyway.)

I have tried using tcpdump included in AdAway but can only see fbcdn.net (and sub domains), etc.; blocking those manually does not help.

I have not yet used tcpdump inside of Termux, for example, to capture traffic to a log file; but I imagine results will be same.

I do not know if Android_external_chromium-webview can be compiled with this "Data Compression" feature and I thought this was a runtime option anyway.

I have also tried to add quite a few other blocking lists ike Easylist and adzblock, etc., to no avail. (I have now removed these to keep only the original 3 lists from AdAway.)

Would really appreciate any helpful feedback as to how to block these "Facebook Audience Network" ads.

Edit: I do not use Facebook nor am I logged in to the website; cookies are cleaned.