The important thing to distinguish here is registered domain vs. remote referrer. Publishers sign up with domains in our network (this being the domain name and parent domain we send over to networks/merchants), with each click they send we get a remote referrer (the literal page the user was prior to clicking on an affiliated link).
Remote referrers we get sometimes can slightly differ from the domains publishers have registered with us. Not only they can slightly differ - but sometimes we do not get any referrer at all (hence coming up as blank).
This can happen for a variety of reasons, publishers may:
- Send newsletters (there is no remote referrer)
- restrictive website policies (which could block this information)
- users open links in a new tab or window (because in the newly opened tab with the affiliated link, there was no page visited before that).
Receiving no remote referrer is pretty usual behaviour and something we see across our network. Providing it doesn't represent 100% of a particular publishers traffic it is expected that there will be some portion of clicks without a remote referrer.