David Rojas posted a link ^ that absolutely had the solution for me. (I reposted the steps below). When I first started experiencing the problem, it felt like hardware, but logically it didn’t make sense since as others said, it didn’t happen while in recovery mode. But as the days rolled on … it seemed like the CPU was spiking rapidly and it was heating up rapidly and it seemed like it was going into thermal shutdown … I found a program that lets you control your fans by your own rules and with that I was able to keep it from shutting down unless it was under extreme load … so that made it feel like a hardware problem, so I did what most techs would do with an 8-year-old laptop … I replaced the thermal compound… but it didn’t fix it… Then I stumble in here and Mr. Rojas had the answer.
Since links go down over time, I’m reposting the steps here that fixed this problem for me:
[quote]'''Reboot into recovery mode holding down CMD+R after boot chime, then open Terminal.'''
[code]csrutil disable[/code]
'''Reboot normally - open Terminal'''
[code](If you have Catalina): sudo mount -uw / ←don’t forget the forward slash[/code]
[code]
sudo cd /System/Library/Extensions
sudo mv AppleThunderboltNHI.kext AppleThunderboltNHI.kext.BAK
[/code]
'''Reboot again into recovery mode and open Terminal'''
[code]csrutil enable[/code]
'''Reboot one last time normally and you’re done!'''[/quote]