Intermittent Resetting During Different Operations

I recently purchased my 7 plus from a friend. He had replaced the screen and home button. So I knew the Touch ID wouldn’t work. But it will restart at random times. It has reset during phone calls, text messaging, and in several other apps. I have noticed that anything done on the phone for 1-2 minutes prior to the reset is not logged. I can be on a call or send a text message immediately before. After the reset you can’t find the call in recent calls. I’ve reset the settings and deleted any apps that were not absolutely necessary. I looked at the analytics but I’m not tech-savvy enough to decipher it. Just wanted to see if anyone had any advice before I try a hard reset or restoring through iTunes.