Can’t establish a connection to the server at

Maybe there is a problem with the server, OOM, firewall... all together or something else. You could start by checking if there was interruption with your server or network problem.

PS: You are italian?

No, but i can fully understand italian language, still expect answers to be in english.

You can explain, please?

If you are losing connection with your server every 30 seconds it could be one of next few problems:
1. OOM (out of memory) - Usually triggered when the server doesnt have enough memory for all the task and then it "kills" some task or the task simply fail to execute.
2. Firewall - It could be the firewall on your server (iptables / firewalld) or firewall from the hosting company that is causing this error, e.g. triggered if you do more than X request in Y time.
3. Network - This problem is more likely to be on the hosting company side and nothing you can do but contact them.
4. All together or something else.

If this problem repeats exactly every 30 seconds you could check your cron jobs and see if there is something what could trigger this connection loss. I mean, if you have same problem every 30 seconds probably is caused by some predefined activity on your server. Check in cron jobs if you have anything setup to run every 30 second up to a 1-2 minutes. Nothing new to see a cron executing something (your server or ext. source) and because the script is slow/broken it will enter in a loop or just eat all available memory (e.g. memory leak).

I would start by checking all your logs and search for any error what could explain what is failing. Only then you can start looking for the solution as right now with the information you provided its impossible to pinpoint where is the problem.

If that was a browser then a problem would occur occasionally and not "every 30 seconds". But you are right and the problem could be triggered by your browser, still i would check all the scripts/plugins what have a problem to load regardless what browser.