Looking at the documentation online, https://www.openproject.org/docs/user-guide/activity/, the Activity shows a sequential number for entries, i.e,

The above shows numbering 3-5. 
However, in our instance of OpenProject (16.0.1), we no longer have the same numbering showing in the Activity entries, 

Is this a mis-match between the documentation and the current version (hopefully not, as the number was very helpful to make references to a previous comment)? Or a setting that needs to be made? 

Thanks!