Yeah, I did that a couple of times before posting in here. The screen continues flashing and only force it rebooted that would get it stopped.
Everything is on the phone after reboot. it is so weird.
I have an old iPhone 5 and bought a new iPhone 7 Plus last week. I am going to sell the old iPhone and want to remove all sensitive data on it. My question is a simple factory reset enough to permanently destroy the data?