Can you share more about your setup? Is it a single heroku instance running off a single database backend? All-in-one server?
This could be an issue if you are using multiple NodeBB instances...
What does this mean ?
I really can't get it
Left Y axis is page views (gray), right Y axis is unique visitors (blue). A page view is just what it say, a visitor looking at a page. A unique visitor is identified by IP. Thus it is a unique IP visiting your site. They are summarized over a day in the graph. Thus every value is per day.
The total you see below is the sum of all page views over the last seven days.