It's probably not traffic shaping, its almost certainly a peering capacity issue between Zen and the major CDNs. Zen probably needs more/better peering with Aka

It's probably not traffic shaping, its almost certainly a peering capacity issue between Zen and the major CDNs. Zen probably needs more/better peering with Akamai and the other major CDNs than they have. I've written more complete answers about this elsewhere in this thread. Hanlon's Razor applies in this case.