In extreme circumstances, a publisher may find that their impressions get locked for a period of time. This is usually as a result of an extremely poor click-through rate and the ad unit has been frozen until somebody clicks on an ad. This is one of our anti-fraud measures that ensures advertisers are getting a reasonable amount of clicks for the impressions being served.

If you find that your impression count is locking, please try to change the placement of the ad unit on your page to increase the CTR.