epochs airflow exporter for prometheus : airflow_dag_status value decrease periodically at 8 o'clock

[Pai-Hung-Cheng]

Hello,
I am new to Airflow and now using Prometheus and epochs airflow exporter to monitor DAG running status.
Below is the link of the exporter:
https://github.com/epoch8/airflow-exporter/tree/master

Recently, I have encoutered a problem when utilizing "airflow_dag_status{status="failed"}" metric.
I find out that value of this metric will decrease by 1 every morning at 8 o'clock, even if there is no dag run for this dag.
I want to know if there is any mechanism for maybe reset this metric, or other reason leading to it.
Thank you!