Ohh, back up for me here in Japan. GitHub's incident team is on crack, that turn around time is quite something. Definitely some impressive stuff.
I'm more used to 'on crack' meaning like 'delirious, over confident'.
In this context though, OP is referring to the drug where the Github engineers are being quick/energetic about fixing the issue because they're "boosted" by the drug's effects.
For example, it would not be out of the question to say something like “when the iPhone launched it was amazing. Like a palm pilot on crack.”
So, when used positively, “on crack” is generally a modifier(in my experience). When used alone it does seem to have negative connotations.
To be on crack is entirely different -- definitely not expert or good.
To be "on crack" is to display any of these qualities; sometimes good, sometimes bad.
I usually see it used to describe a positive trait in the form of high energy / confidence.
To explore the quirks of English grammar a bit further... While "the general expected this to be a crack team of commandos" flows fine, I've never seen "the general expected this team to be crack".
Perhaps it's similar to the rules for the adjective "top"? One can have a "top team of athletes", but "this team of athletes is top" doesn't work, it needs to be "topmost" or something.
IANAGrammarian, but it's almost as if "crack" isn't being used as adjective that modifies "team", but instead they've merged to become a single noun of "crack-team"... kind of like how "first-responder" is a category of emergency-related jobs rather than literally any person who happens to be the first to arrive.