One of the referrals that I was receiving a weigh bonus is no longer showing up as a "Referral." I just noticed an add for that referral's website, checked their site and they are still showing the network ads. Is there a time limit for how long you will receive the weight bonus for a referral?
No, you get weight bonus forever. If it's not showing as a referral any longer, their account may be deactivated for whatever reason (not showing ads on all pages for example).