Yeoman, webApp, bootstrap 4, "grunt serve" fails

I created a WebApp with Yeoman, selecting "bootstrap 4". When it finishes (Without errors), I try to "grunt serve", and I get the disgusting error:

$ grunt serve
>> Local Npm module "grunt-autoprefixer" not found. Is it installed?
>> Local Npm module "grunt-contrib-connect" not found. Is it installed?
>> Local Npm module "grunt-contrib-cssmin" not found. Is it installed?
>> Local Npm module "grunt-contrib-htmlmin" not found. Is it installed?
>> Local Npm module "grunt-contrib-jshint" not found. Is it installed?
>> Local Npm module "grunt-contrib-uglify" not found. Is it installed?
>> Local Npm module "grunt-contrib-watch" not found. Is it installed?
>> Local Npm module "grunt-mocha" not found. Is it installed?
>> Local Npm module "grunt-newer" not found. Is it installed?
>> Local Npm module "grunt-svgmin" not found. Is it installed?

Running "serve" task
Warning: Task "autoprefixer" not found. Use --force to continue.

Aborted due to warnings.


Execution Time (2017-03-16 08:49:10 UTC)
loading tasks  383ms  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 99%
Total 385ms

Things I have already tried:

• npm install
• bower install
• sudo npm install grunt
• chown -R 'username' ~/.npm (I replaced 'username' with my username)
• sudo chown -R $(whoami) ~/.npm
• sudo grunt serve (just had to try)

Basically, after scafolding the app, I used this to code and see the results immediatly as the file got saved it got updated. It's been broken for several months now. Thanks for your help!

P.S.: I have searched a lot to find an answer to this question, without luck.

via Josep G