Answer to "Randomly shuts down when not connected to an external display."I just installed a Samsung 970 EVO NVME SSD with adapter and the shutdown issue is gone without deleting the kext AppleThunderboltNHI.kext
Answer to "Randomly Black Screens and powers down."Reapplying thermal paste of the cpu helped in my case with the same machine for 100%
Answer to "Randomly shuts down when not connected to an external display."Workaround: I have the same issue with my MacBook Pro 15 Mid 2014. The only way to use the MacBook without the shutdown problem is using an external display or a HDMI dummy plug like this: https://www.amazon.de/gp/product/B072PV6... It is a hardware defect on the logic board, probably the i7 Processor with intel Iris Graphics. Maybe its the smc circuit. On Windows, I thought, I had no problems. But I saw some times the display goes black for 1/10 of a second. So I believe, it is the defect of the Onboard Graphic. My Problem occurred, when I used dolphin Nintendo WII emulator, which leads to 100% CPU usage und the fan full power. I think, the MacBook went too hot and this caused the damage.