000 in a Squid Log Is Not a Website Response
Read a zero HTTP status beside the connection lifecycle and probe behavior before assigning a root cause.
There is no ordinary HTTP response status called 000. In Squid's access log, a zero in the HTTP-status field means that an HTTP result was not available for that transaction.
Read it with the surrounding result code, duration, byte counts, client and requested operation. A health probe that opens a socket and closes it is doing something different from a browser completing an HTTP request.
Match the timestamp to the actual probe configuration. Old monitoring instances can continue sending checks, and a short probe timeout can close the connection before the expected exchange finishes. Those are possibilities to establish, not conclusions encoded in 000.
Consult the internal log and host evidence if the record points toward a broader stall. A historical case involving storage delays does not make storage the explanation on another server.
Changing a log parser to call 000 a website outage only hides the ambiguity. Keep it as an incomplete HTTP outcome until the connection evidence explains what happened.