Alert rule is not delivering all alerts into PD, only 1 alert receive all the time

The alert rule defined to monitor pvc disk usage and send to PD when alert triggers. We expected to receive two alerts if there are two pvc disk usage is at low capacity. However, we are only receive one alert from PD despite there are two are alerts triggered. the second alert never delivered.

We have the grouping disabled on the notification police and there is no grouping from PD side either. Is anyone know how to check whether grafana logs to see if the second alert has been sent or get stuck somewhere?