Apple SVP of Software Engineering Craig Federighi in an email reply to a MacRumors user:
We regretfully had to temporarily drop support for this gesture due to a technical constraint. We will be bringing it back in an upcoming iOS 11.x update.
Thanks (and sorry for the inconvenience)!
I’m glad to see this coming back, but I wonder what the technical constraint was. Maybe something to do with iPhone X? Speaking of which, I wonder if it will even be enabled on iPhone X; it’s much less needed there due to the new navigation gestures. Either way, I’ll enjoy seeing it return to the iPhone 7 I use for work.
One other thing they need to bring back is quick access to Spotlight Search from Notification Center. I’m not talking about the existing one in the Today/widgets view, but the one where you could pull the Notification Center shade down just a little bit, release, and get to Spotlight Search. I used this so much to quickly get into another app.