'502 errors are due to healthcheck setup or resource exhaustion

My setup is a bitnami wordpress hosted on GCP's N2-standard-2 VM. I'm using a HTTPS load balancer and CDN.

I encountered the 502 errors a few times ever since I configured a load balancer. I was doing quite a bit of seo and page scanning tests when this happened.

I've checked that the VM is only using 8-12% of the disk capacity. The log shows CPU Max usage is 9.62%. I've to restart the VM to resolve the error.

What are the cause of the 502 errors

Could it be due to the traffic spike from third party scanning sites?
Is it because of my health check configuration?
Do I have to change a machine type and increase the memory?

What should I look into to troubleshoot it?

This is my healthcheck setup This is my healthcheck setup

The server was down again and this time round I managed to look for the information you have suggested.

The error is not from Load Balancer
The error is from VM and the error message is: "Error watching metadata: Get http://169.254.169.254/computeMetadata/v1//?recursive=true&alt=json&wait_for_change=true&timeout_sec=60&last_etag=ag92d16ff423b06: net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)"
VM disk size is 100GB. Machine Type is N2-standard-2 VM
It is a Wordpress Instance
Everything is within Quota
Incidents happen on a few occasions:
- when I use third party site to scan the website for deadlinks. After the scan is completed, the server will go down shortly after. I have to reboot the instance to make it functional again.
- It happens randomly and recover by itself after a while

Thanks everyone for your help. I just managed to figure out how to retrieve the other required info.

I was wrong that the load balancer didn't report any errors.

Below is from Logging

From Loadbalancer : Client disconnected before any response
From Loadbalancer: 502 - failed_to_pick_backend
From Unmanaged Instance Group: Timeout waiting for data and HTTP Response Internal server error

I tried to increase the Load Balancer timeout duration, the VM stills shut down and rebooted on its own. Sometimes it takes a few minutes to recover and sometimes it takes about an hour plus.

I provided some screenshots which recorded the recent incident from 8.47 to 8.54.

Below is from Monitoring