Netguard do not block all requests, but only some...
Since I was surprised to see that some applications, supposed to be 100% blocked, were nevertheless consuming data, I did a quick test :
I blocked two applications for which I can "see" on the screen if they succeded, or not, in getting data.
The first one is OruxMaps, that is a Map viewer, getting map "tiles" (small piece of image) from various servers, to display maps.
When it is supposed to be 100% blocked, it has nevertheless access to some Internet data, while some other are blocked.
I've not been able to see what could differ servers that Netguard (correctly...) blocks and those that it let pass.
It is not due to the port (some http / 80 pass, some are blocked, some https / 443 pass, some are blocked)
For example, all tiles provided by server
http://a0.ortho.tiles.virtualearth.net are blocked, while those on server
http://h0.ortho.tiles.virtualearth.net are accessed !!
If I set the option of journalization and filtering, access attempt is reported for the blocked server, while nothing for the other server....
Of course, if I de-activate NetGuard, tiles from both servers are OK.
Then I did a second test : I blocked "Samsung Internet" browser itself.
And here again, some sites can be nevertheless browsed, while some other are blocked.
Example : no problem to browse
http://www.lemonde.fr or
https://www.ledauphine.com, while it is impossible to browse
https://fr.m.wikipedia.org ....
And also with browser, it is possible to get
http://h0.ortho.tiles.virtualearth.net/tiles/h120220333311.jpg?g=45 while
http://a0.ortho.tiles.virtualearth.net/tiles/h120220333311.jpg?g=45 is blocked !
And also with browser, blocked accesses are reported (and nothing about unblocked ones)
And also with browser, all requests and browsing are OK if NetGuard is deactivated.
I precise that I am on a Samsung Galaxy A3 2016, Android 7.0, NetGuard 2.281