It looks like puppeteer doesn't like you calling page.setViewport before having any content loaded.

If you do it looks like page.close() is called.

If anyone is trying to debug problems with puppeteer I recommend starting it with this line from a shell:

env DEBUG="puppeteer:*" node puppeteer_script.js "$@" <&0

This should help you find the problem. Having used puppeteer twice I have found it rather picky on the order you run things.