What does it mean when adplexity shows an ad's affiliate network as 'None'?
In most of the cases that mean that the network is new for Adplexity and not yet included in the database, but still can track the offers from it. You can find which network it is by checking the redirection chain, and look for the outgoing URLs.
Could it also be the case that an affiliate (or network) is running the ad directly with the advertiser?