My 7 has had it since GM, can’t remember if on any of the betas.
I don't think it's a bug, but it only appears if your phone isn't passcode locked or you have a passcode timer.
It is a bug & a low priority one. It has been there since ages. Sometimes it messes up app that are meant to lock only on portrait mode.
Of course they do.Even Plus models don't have that.
Seems like the issue here isn't the lock screen use of Notification Center, but the landscape orientation that shouldn't apply to non-plus phones.This is new Notification Center design in iOS 11, not a bug.
It just "looks like" a lock screen. If you press the power button to lock screen, it will return to normal design.