Ubpv cookie disappears after successful click through goal

I’m trying to use the ubpv cookie to register a lead using php. The cookie shows up on the unbounce landing page, but disappears when I browse to my regular site, though the ubvt cookie stays. The permissions are all correct and I should be able to access it from the main domain as the path for the cookie is /. Does anyone know why this happens? I’m trying to keep track of my variants, but I only have one champion variant active. I can’t find any documentation about the technical details of this cookie.