Omni Channel - Maximum number of cases queued, but not routed

You should try to review the load of items in the queue. To do this please run the below query either in Developer console or Workbench to see the number cases that are in the queue.

To check the current number of items pending in a queue, run the following query in Developer Console or Workbench.

Query:
SELECT count() FROM PendingServiceRouting WHERE QueueId = "Id of the queue".


Please define the Overflow Assignee in the routing configuration so that when the limit is hit, new records gets assigned to specific Queue/User to avoid the error.

To learn more about Overflow Assignee, please refer to this article.