React built with concurrently.js not finding build command [react-scripts: command not found]
This is not a create-react-app issue, is a npm one. Check this link https://github.com/npm/npm/issues/17379
UPDATE: It seems this is just an inconsistency between yarn and npmhttps://github.com/npm/npm/issues/17379#issuecomment-358434577
You can try to remove node_modules and package-lock.json or yarn.lock
And execute npm install again.
Or you can downgrade npm to 4.6.1 that does not have the issue
npm -g i npm@4.6.1