When the PCRF explicitly disables Usage-Monitoring on the node, the node reports the accumulated usage which has occurred while Usage-Monitoring was enabled.
To disable Usage-Monitoring for an entity, the PCRF sends the Usage-Monitoring-Information AVP referencing only the applicable monitoring entity with the Monitoring-Key AVP and the Usage-Monitoring-Support AVP set to USAGE_MONITORING_DISABLED.
When the PCRF disables Usage-Monitoring in a RAR or CCA command, the node sends new a CCR-U with the Event-Trigger AVP set to "USAGE_REPORT" to report the accumulated usage for the disabled Usage-Monitoring entities.