Error 502 Bad gateway - random and only on certain subdomains

Sorry, i don’t understand…

It is not like www.[third-level-domain].SLD.TLD versus [third-level-domain].SLD.TLD but its about different third level domains.

Why do you think in that way?

I mean, i’m talking about the same third level domanis.

. subdomain1 with and without WWW has different behaviour. (502 without WWW - FINE with WWW)
. subodmain2 with and without WWW has same behaviour (FINE with and without)

So, just talking about the URL with erros (same subdomain)
http://subdomain1.mydomain.com --------------> 502 BAD GATEWAY
http://www.subdomain1.mydomain.com --------> WORKS

Maybe there is something i missed?

are you absolutely sure the hosts in question really point to the same IP? Can you double check?

Sure,. I’ve got only one public IP.