I've added a minimal test repo at https://github.com/alexhillel/gsap-test-case - running node 10.3.0 and npm 6.1.0 on my Mac:
npm install
npm run production
results in:
ERROR Failed to compile with 1 errors 7:47:34 PM
error
/scripts/main.js from UglifyJs
Name expected [./node_modules/gsap/TweenLite.js:1966,0][/scripts/main.js:2045,6]
Asset Size Chunks Chunk Names
/scripts/main.js 382 kB 0 [emitted] [big] /scripts/main
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! gsap-test-case@ production: `NODE_ENV=production webpack --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the gsap-test-case@ production 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! /Users/alexhillel/.npm/_logs/2018-05-30T18_47_34_790Z-debug.log