Not sure if it helps, but here is another log:
sudo cat /root/.npm/_logs/2018-09-19T11_12_49_127Z-debug.log
0 info it worked if it ends with ok
1 verbose cli [ '/usr/local/bin/node',
1 verbose cli '/usr/local/bin/npm',
1 verbose cli 'i',
1 verbose cli '-g',
1 verbose cli '--unsafe-perm',
1 verbose cli '--no-progress',
1 verbose cli 'node-red@latest' ]
2 info using npm@6.4.1
3 info using node@v8.12.0
4 verbose npm-session 5707cdbfa0265a3c
5 silly install loadCurrentTree
6 silly install readGlobalPackageData
7 verbose stack TypeError: asyncWrite is not a function
7 verbose stack at onwrite (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:480:7)
7 verbose stack at WritableState.onwrite (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:180:5)
7 verbose stack at WriteStream.to [as _worker] (/usr/local/lib/node_modules/npm/node_modules/pacote/node_modules/make-fetch-happen/cache.js:154:13)
7 verbose stack at WriteStream._write (/usr/local/lib/node_modules/npm/node_modules/mississippi/node_modules/flush-write-stream/index.js:35:13)
7 verbose stack at doWrite (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:428:64)
7 verbose stack at writeOrBuffer (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:417:5)
7 verbose stack at WriteStream.Writable.write (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:334:11)
7 verbose stack at WriteStream.to [as _worker] (/usr/local/lib/node_modules/npm/node_modules/pacote/node_modules/make-fetch-happen/cache.js:171:25)
7 verbose stack at WriteStream._write (/usr/local/lib/node_modules/npm/node_modules/mississippi/node_modules/flush-write-stream/index.js:35:13)
7 verbose stack at doWrite (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:428:64)
7 verbose stack at writeOrBuffer (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:417:5)
7 verbose stack at WriteStream.Writable.write (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:334:11)
7 verbose stack at WriteStream.to [as _worker] (/usr/local/lib/node_modules/npm/node_modules/pacote/node_modules/make-fetch-happen/cache.js:182:19)
7 verbose stack at WriteStream._write (/usr/local/lib/node_modules/npm/node_modules/mississippi/node_modules/flush-write-stream/index.js:35:13)
7 verbose stack at doWrite (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:428:64)
7 verbose stack at writeOrBuffer (/usr/local/lib/node_modules/npm/node_modules/readable-stream/lib/_stream_writable.js:417:5)
8 verbose cwd /home/pi
9 verbose Linux 4.14.69-v7+
10 verbose argv "/usr/local/bin/node" "/usr/local/bin/npm" "i" "-g" "--unsafe-perm" "--no-progress" "node-red@latest"
11 verbose node v8.12.0
12 verbose npm v6.4.1
13 error asyncWrite is not a function
14 verbose exit [ 1, true ]
