So, the state as-is looks like this:
The only Android app that kept its connection to the internet is Whatsapp, just because I didn’t clear out its cache and application data. Instagram worked until I decided to try and flush its app memory. Also, while WA still works, it has lost its connection to Giphy.com (so now it is unable to fetch Gifs - I don’t need it, but maybe it helps to pinpoint the culprit). Gifs received via WA messaging can be opened and sent, so it is not a data type problem but a connection-to-the-web one.
No store (Aptoide, FDroid, Aurora) works, Android App Support setting puts the “no internet” tag on every WLAN I connect to, and mobile data connection also doesn’t work (for the Android side, all native Sailfish apps are working flawlessly).
So far I tried: restarting App support, restart network (both SFOS and App support independantly), uninstalling and reinstalling Android Compatibility layer, restarting the phone multiple times, reinstalling single apps. The APN is set as it is on the SFOS layer, and tinkering with it didn’t improve anything. Also, having Tor active or not doesn’t change a thing (it only seems to affect SF browser anyways).
So far, my guesses are either some kind of pass-through issue through the Android compatibility layer (like some kind of closed ports or tunnels), changed connection/handling routes either on the connman or Droid side, or else (I mod humans, not technical devices).
I’d like the Android side to regain network access again (the printer app only needed a local WLAN connection without internet access, which isn’t possible atm, so it has nothing to do with the internet itself), that’s all.
Are there any logs I could collect and post here to help solve the problem? Unfortunately, NielDK’s compiled Wireshark application doesn’t install anymore, so I cannot rely on this like in my Jolla Phone days 
Cheers.