It has been noted in the Enforce management console that the Incident Queue for your Cloud Detector is stuck at 1000 and doesn't seem to be changing.
Release : 15.x
Component : Cloud Detection Server
The DLP Cloud Service is a hosted service which integrates with the Enforce console - itself a managed on-prem installation.
In contrast to on-prem Detection Servers, the Incident Queue for a Cloud Detector currently reports a maximum of 1000 incidents queued.
The backlog as such is related to how many incidents have been created on the Detector, but is also dependent upon the Enforce server's internet-connection speed to the Cloud Service Gateway, and on the resource availability for the Enforce DLP services processing incidents.
Also, for customers on DLP 15.8 MP2 or earlier see the following KB: Incidents from the DLP Cloud Service are stuck in queue (broadcom.com).