That can happen if you create pages in an scheduledjob where you don't have an usercontext.
Maybe you have a scheduled task that performs page changes which is anonymous?
Not sure if just created pages, where the editor has not marked the page as changed, has the property set.
We regularly run reports to see who has changed what pages in our organisation - however some of the Changed By fields are blank.
Anyone know of any reason why this could be?
As always, Many Thanks.