Is this a bug, or are we really losing traffic that badly?
There are two questions on Meta StackExchange about this:
A comment on the first question by Dean Ward, software developer for Stack Overflow, says:
We're investigating, we've had a number of large changes to our Google Analytics infrastructure, looks like we missed some bits...
Update 03.07.2018: It appears that Stack Exchange fixed the traffic statistics issue today or yesterday, at least in Area 51, which currently says we have 1,484 per day (very close to the 1,500 visits per day that is considered "good").