Check whether you have created customized priority rules and configured them for tracking visitors in the priority circle. If you have not created any priority rules, check whether you have exceeded the default limit specified for the number of visitors to be tracked in the SalesIQ application. 

The number of visitors you can track by default is 200k. If you have exceeded the default limit, you will not be able to track your visitors. You can purchase additional add ons to increase the default limit.