Is it possible to hack an Android device while the victim is using vpn? I've tried hacking my Android device on WAN and it worked but when I connected my cellphone to a vpn network it seemed that the session was unable to be opened . Now I'm wondering if there is a way by which Android devices can be hacked while they are connected to a vpn network.
Your question is a bit abstract and might have different answers.
My answer will focus in a specific situation that happens in vpn connections.
It will depend on the vpn type. If your vpn has no split tunnel it means that the default gateway of the connection will be the vpn. That might create some issues as the packets will be forwarded to the new gateway and not to the wan.
Depending on the vpn you might have a non straight forward way to connect to Internet and thus causing issues in reverse shells or bind shells for example.