On my Samsung S8 with Android 8.0.0, Orbot starts automatically on boot. Although it connects successfully to the Tor network, my apps cannot connect to Tor until I manually turn VPN Mode off and on. I had the problem with Android Nougat, too. I had been experiencing the problem on Sony Z3 Compact (Nougat) and LG L90 (Lollipop) too. But LG X-Power with Android 6.0.1 works fine.