Are they following the MarketForce path where they remove shoppers at some point?
How many shops have you skipped after grabbing them as part of the I Shop First program? Could that have triggered a deactivation? I'm not saying you did this, but I know some shoppers do, so maybe that could be a resaon.
I would think if you emailed one of the project schedulers directly, you would get an answer. Please keep us updated here on the results.