Restarting studies is taxing to the CloudResearch system that communicates with Mechanical Turk. Thus, all studies are currently limited to 200 restarts.
Restarting your study is an MTurk specific way of making sure that studies that have been live for awhile remain visible to workers. Whenever your study restarts it is moved to the top of the Worker Dashboard. Restarts can occur manually by pausing and restarting your study or automatically when you use MicroBatch or HyperBatch.
The current maximum for restarts is 200. If your study reaches 200 restarts and still has not collected your desired sample, your sampling criteria may be too narrow. To check you can contact our customer service or if you wish to continue with data collection you can copy the study, exclude the original study from the clone, and launch your new study.