I’ve got the same issue in my development environment. I’ve tried two different Vagrant setups (VVV and Trellis/Bedrock by roots.io). The page builder doesn’t work in either of those. I found some post about enabling script debugging in wp-config but that didn’t do anything for my dev environment either, and I wouldn’t like to do that in a production env anyhow. Screenshot below.
I double-checked if I was blocking any necessary JS files, and I’m not. I am getting some errors in the Web Dev Console though, see my second screenshot.
EDIT: This only happens on Pages, not on Posts.