This can be caused by several different things.  Some suggestions to consider:

First check to make sure you have not applied any routing filters to your callers. To verify this go to Routing --> Routing Filters. If there is anything listed beside the caller’s name remove it by clicking the edit button.

Second make sure that the calling periods are properly set up on the Calling Periods page (under Routing). Remember that if calling periods are on, contacts with no valid phone number will not be routed.  Also check to see if your lunch times are being restricted.

The Flagged Contacts page (under Routing) is designed to help you troubleshoot routing problems. It will display how many contacts are flagged to be routed, divided by team (if appropriate), and indicate how many are available to be routed at that exact moment based on calling restrictions. This information can help determine why certain callers are not receiving contacts.