None of the above helped me, but the comments about hostnames lead me to find my solution. I had to change my computer name for security reasons, so changing it back was not an option.
What fixed it for me was to:
1. De-authorize my macbook (I did this on line6.com)
2. Delete these folders to totally remove Native and all user settings:
"${HOME}/Library/Application Support/Line 6"
"/Library/Audio/Plug-Ins/Components/Helix Native.component"
"/Library/Audio/Plug-Ins/VST/Line 6/Helix Native.vst"
"/Library/Audio/Plug-Ins/VST/Line 6/Helix Native.vst3"
"/Library/Application Support/Avid/Audio/Plug-Ins Line 6"
3. Reinstall Native, login and authorise computer (I actually used the line6 license manager to authorise the computer before reinstalling Native)
I wrote a simple script to achieve the above. Maybe it will be of some use to someone else. See my github gist: https://gist.github.com/Huevos-y-Bacon/93b59173945137523cab9a46335c34b3