`npm install -g node` removes node

[serapath]

npm -v was 6.11.2
node -v was 12.9.1

I'm running npm install -g node and get:

npm WARN lifecycle npm is using /home/serapath/.npm-global/lib/node_modules/node/bin/node but there is no node binary in the current PATH. Use the `--scripts-prepend-node-path` option to include the path for the node binary npm was executed with.

> node@12.9.1 preinstall /home/serapath/.npm-global/lib/node_modules/node
> node installArchSpecificPackage

sh: 1: node: not found
npm ERR! code ELIFECYCLE
npm ERR! syscall spawn
npm ERR! file sh
npm ERR! errno ENOENT
npm ERR! node@12.9.1 preinstall: `node installArchSpecificPackage`
npm ERR! spawn ENOENT
npm ERR! 
npm ERR! Failed at the node@12.9.1 preinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/serapath/.npm/_logs/2019-09-01T23_36_49_888Z-debug.log

how and/or why is this happening?

I quickly re-install the latest npm and node version with a little bash script:
https://github.com/serapath/node-and-npm/blob/master/install

...but afterwards, running npm install -g node causes the same issue again. The script itself actually even uses the very same commands to get and update to the latest versions so i'm very confused.

any pointers? :-)