That's a good question.. I can't find any reference to this...
Do you have mobile app data in your suite (where maybe the URL isn't being set), or maybe the first "hit" of the visit was on a click where the URL is stripped?
Is there any other contextual data in the row that might help diagnosing why you are getting a numerical value instead of a URL? Do you have any processing rules or vista rules that might be overriding some values?
@valerie_anders- Could it be a possibility that we are reading data incorrectly? While reading, the value from some other column probably shifted to visit_start_page_url giving an impression that visit_start_page_url=1, it could be a value from columns like visit_page_num or visit_num showing up in that column. Just a thought! If you think that's not the case, try reaching out to Customer Care for further investigation. It will be really interesting to know what that is, as I haven't seen it yet.