You must enable always-on VPN killswitch in Android VPN settings, and put Invizible in VPN or root mode, instead of proxy mode.
Rethink dev has spoken to me multiple times. He has made a very good app, even incorporated changes I recommended, but it can stop functioning at times abruptly, according to a fellow friend who tested it thoroughly. Invizible is more stable, so I am yet to change recommendation, since I recommend Invizible for heavier, hardcore setup and NetGuard for easier, relaxed setup. I am currently off of Invizible after 3ish years and daily drive testing NetGuard to see how well it is working.