Network received bytes on Cloud Run is 0 B/s

[vinafy]

Hi! I'm deploying a machine learning based application that displays a recommendation of something to Cloud Run and Cloud Functions. This application uses flask API to handle HTTP request and response. However, when monitoring network performance, the network received bytes returned a value of 0 B/s during the test. Does anyone know what causes this and how to fix it?

Dashboard monitoring:

 

Metrics used:
run.googleapis.com/container/network/sent_bytes_count
run.googleapis.com/container/network/received_bytes_count

Thank you!