Tracking will work on every domain, but a lead has to be cookied for each domain separately. So if you have Domain1 and everyone's cookied for it, and Domain2, you will need a registration form or tagging email campaigns in order to ensure that Domain2 is cookied.
I have 4 sites. I only track one. When I view my web activity reports for my HRM website, because they is no form on the site, no one ever gets cookied. So all my reports are anonymous leads.
If you're saying that your leads aren't being tracked at all, no visits, then create a ticket for support.