EDIT: it's happening again today on Meta Stack Exchange; the last Traffic data point is from Monday, November 18th, more than two days ago. On Chess.SE, the last data point is November 20th, as expected.
There's something wrong with some of the information on the site analytics pages across the network. It's November 6th, and the date selector on top of the page says the data is up to November 5th:
Yet on some sites like Meta Stack Exchange, Chess Stack Exchange and Board Games Stack Exchange, the latest data point for traffic is November 3rd:
The arrow indicates the data point I'm hovering over and the corresponding (misplaced) tooltip.
For votes, the latest data point is November 4th; posts are up to date.
On Ask Different, the situation is slightly different; new visits are up to date but the last data point for page views and visits is November 2nd:
I think it used to be up-to-date in the past; the screenshot in this old bug report of mine was made on April 11th and shows data points (though with the wrong values) up to April 10th.