OpenSearch Alerting module Alert count does not match instance occurrence

With respect to OpenSearch Alerting module, we have seen that if a condition is met for multiple objects/instances at the same time, the number of Alerts it generate does not match the instance count. Ex. If we have created a rule for Device Down Alarm and in real time if 10 devices went down we expect it to create 10 Alerts, but we found random behaviour that is sometimes 6 Alerts were created and sometime 7 but it never match the instance occurrence. Can you please help us out here.