My website can’t be reached, but nothing wrong on GCP

Error message: webiz.johocen.com took too long to respond. But there is nothing wrong on GCP VM instance. ping webiz.johocen.com got 0% lost 169ms average response

My website is a WordPress multisite on GCP via bitnami. This happened before, reset the VM will solve the problem, but will happen again sometimes later.

Any suggestion where I should look into... Thanks