While developing with create-react-app, my browser enters debugger mode on warnings:
It breaks on the source code of react-dev-tools:
Based on pull request DevTools: Make break-on-warn off by default #19309 it seems it's a bug.
The Break On Warnings box was unchecked for me and it still would break. Removing and readding the extension to force an update fixed it for me.
I don't know of another way to force Chrome to update an extension outside of its regular schedule.