My Android (Samsung Note 4) keeps disconnected after a while from a sign-in required wi-fi
I've searched and it seems this problem is not related to VPN. It's a capabilyty/Bug [at least] in some android devices (esp Samsung) which turn off the wifi when it found it not connected (without considering the simple fact that it might have connected through a vpn!). So this is a Bug. It seems this helps somehow.

In a nutshell current solutions are these:


Block client3.google.com in your router
Fool your device by setting up face proxy (then the sign-in required message goes away) and then modify it to none proxy again
disable wifi assisted location