I can confirm the ApplethuderboltNHI.kext fix does work on Catalina, even up to 10.15.1. I have had no random shutdown since the fix, 22 days ago. Before the fix, the shutdowns were happening every few minutes and nearly drove me mad.
I did the fix while I was on 10.15 and everything was fine for 22 days. But I recently updated to Catalina 10.15.1 and the shutdowns started happening immediately after updating. This is because the ApplethuderboltNHI.kext is re-added every time you update the OS. So I had to go through these steps again:
- Restart with Command+R pressed, release when you see the Apple logo, then login
- Open Terminal from Utilities menu
- Run: csrutil disable
- Restart in normal mode
- 4.5 (if running Catalina) run: sudo mount -uw /
- Run: sudo mv -i /System/Library/Extensions/AppleThunderboltNHI.kext /System/Library/Extensions/AppleThunderboltNHI.kext.BAK
- IMPORTANT: You may have to type this in manually and just drag the file into the terminal to get the file path, then add .BAK at the end. Otherwise you may get a "usage: mv [-f | -i | -n] [-v]..." message. Also remember the directories are Case Sensitive.
- After you run this command and get no errors or messages, open Finder and go to /System/Library/Extensions/ and double check that AppleThunderboltNHI.kext.BAK is there. It will look like a folder. That means the rename was successful.
- Restart with Command+R pressed
- Run: csrutil enable
- Restart and forget about the problem
These steps worked for me on Catalina 10.15.1 and my late 2013 rMBP 15" is solid once again!
If this is working on Catalina, it should still work on Mojave, even on the latest version. If you don't want to upgrade to Catalina, try these steps again.