Usually this would be caused by one of these issues:
- The tracking code is not on all pages of your web site. Check all site templates, landing pages, etc. If a visitor lands on a page with no code, then it would look like they came from that page when we first see them on a page with the tracking code.
- You have multiple sites / domains, such as www.yoursite.com and signup.yoursite.com etc. These are seen as different web sites by the browser.