There may be some existing requests which have not included page numbers. You can find these requests by selecting "Missing page numbers" option from the "Requests" menu. In the actions menu for those requests, selecting "Set page range" will present a window which will allow you to address this.
Alternatively, if you visit the request detail page for any request which does not have a page range, there will be a warning to indicate this, with the option to "Set page range".