Def seeing a pattern here in their ad server. What if you launched a campaign let it run for 2 days, then each day you were simply re-launching from fresh? Some ad servers will automatically assume that your eCPM is going to be crap and drop you from the chain. This specifically was true with MySpace MyAds. I can remember going in and creating THOUSANDS of ads because no matter what my CTR was the ad server always assumed the eCPM was going to be crap. So I simply re-launched every day, paused, rinsed and repeated. Based off your clicks, ROI drop, I feel like something very similar is going on here.
Let me know if we can try that and we'll see what happens!