Does not work with firewall

I have installed a VPN based firewall (Netguard) which blocks most apps from internet connection. A similar app (Rethink DNS) which does the same which is a combination of an app blocker and a Wireguard VPN. When I use that firewall instead of Netguard, the issue is the same: no internet on Native Alpha (whitelisted), but internet does work on other whitelisted apps.

A few weeks ago it was no issue, but since a couple of weeks this app (and Hermit which is similar) does not load any webpage. Obviously I have whitelisted this app and Hermit. Both apps use Android Webservice, so I whichlisted Android Webservice as well, but to no avail.
In other whitelisted apps (such as the Firefox based Iceraven) internet is normally available.

Is it an issue of this app or does Google Android webservice block the use of firewalls ?