Walk through the network path from DNS to HTTP and find where things are breaking.
Browser JavaScript cannot do raw ICMP or arbitrary TCP — reachability and port checks run server-side via this site's APIs. Results reflect this server's network path.
Can the hostname be resolved?
Is the host responding?
Is HTTPS port open?
Does the server return HTTP?
Is the certificate valid?
Each step is honest: passed, failed, skipped, or unable to check. The diagnosis at the end is based only on checks actually performed — it says "most likely" when evidence is partial. Fix the first failing step, then re-run.