2014 MBP spontaneously rebooting

Specs: MacBook Pro, 15", retina, Mid-2014, 2.2 GHz i7, 16GB RAM

OS: 10.13 High Sierra, problem also persisted on 10.12 Sierra

The problem I am having is that the MacBook reboots spontaneously. In the last two days it has happened nine times and over the past month it's been happening a few times per week. The reboot occurs without warning and I do not receive any sort of error report or warning when I boot the computer back up. The problem usually occurs when I am using a web browser, but that is my main use for the MacBook and it has persisted across multiple web browsers.

Solutions I have tried:
-Took it in to the Apple Store last month, no problems were initially found

-Formatted the hard drive at Apple Store and reinstalled all software

-Reset SMC

-Reset PRAM

-Ran diagnostics, everything clean

Now I'm posting here. I'm not sure what else to try, hopefully you all can point me in the right direction.