I've just made a fresh vagrant install with Scribunto, and I've noticed that the debug console isn't showing up. Looking at the web console in Firefox, it shows "TypeError: mw.scribunto is undefined" (stack trace). I assume this has something to do with Gerrit 186503, which just got merged.
This problem is also occurring on Beta Wikipedia. For this reason I assume it's going to hide the debug console on mediawiki.org and the test wikis later on today when the rollout happens, so I'm marking this as top priority.