In GCP load balancer monitoring, what is "unhealthy network traffic"?

I'm running an Google CloudRun instance for an API. Today I've added a load balancer in front of it, so that I can set an SSL Policy that disallows TLS <1.2.

In the screenshot below, it appears that the traffic I'm getting from America is "unhealthy", and now warning icons are shown next to the different parts of my infrastructure. I'm pretty new to this area of GCP and I'm finding the docs impenetrable. When I googled unhealthy traffic, it took me to a page for creating health checks, which I did, but my backend service won't allow me to add a health check, the option is disabled with no apparent explanation. As far as I can tell, these health checks are for ensuring that your backend service is up and running? Mine is, it's handling requests just fine.

So does "unhealthy" mean something different in this context? ie, it doesn't seem to be related to whether the backend service is up?

I would be really grateful if someone could point me to something that explains what "unhealthy network traffic" is, how much of a problem it is, and how I rectify it.

Sorry this is a vague question - I'm not sure what specific information is useful to include.

I tried to find some documentation that would explain what this "monitoring" panel actually tells the user but couldn't. There's only the legend on the bottom of the screen.

I'd recommend filing a feature request on Google IssueTracker to point to some documentation and make this page more informative. Describe in detail what you wold like to see there and how to you expect it to work.