virustotal results

Not sure i follow.

It scans a domain through various AV engines and then tests the domain in a sandbox, it gives a full rundown of what the browser and its relevant areas of the computer are doing when the browser connects to the given domain. it then checks that information against a database of known attack vectors.

MITRE ATT&CK(R)

Not sure how it would timeout your server unless you mean your browser timed out.

503 is actually a catch all and it can be very well often tied to something that is timing out like a connection or request. Subsequently it precedes 504 which is an actual timeout error but this is only coincidence because 503 is catch all.

regardless it was a generalization when i said it as result because 503 is one, further in one that can be caused by timeout.

The whole category of 5XX errors is basically for discrepancy like partial knowing something is wrong but throwing a generic 5XX code because there could be bad error catching or bad things on the client. Were as the ones before that is hard line in the sand.

generally
5xx - knows something is wrong but not always sure what to do
4xx - Client side, knows that the client is having issues
3xx - Redirection

etc

the actual 503 definition is for taking to long for the server to return that information but that is not all it is for and in
your case the client is in the way of itself.