Ive tried so far generation 1 and 2 machines. Always a fresh installation. Just cant connect through https ( NET::ERR_CERT_AUTHORITY_INVALID) or through http (ERR_CONNECTION_RESET).
Thought my nic might have given up so i went ahead and created an ubuntu 18.04 server and it worked like charm.
This is perfectly normal–Nethserver generates a self-signed certificate on installation. Your browser will allow you to create an exception or otherwise proceed to the server manager, where you can install a trusted cert if you choose. Edit: I’d also note that this is a completely different error than you reported up-thread.
…to do something completely different. You’re comparing Apples with Chevrolets.
Access to the server-manager through http is redirected to https. As has been already said the warning message is shown because initially it is using a self-signed certificate.
If your are using Chrome, there use to be an option to proceed to the site anyway (Advanced > Proceed to…). Similar options are available in other web browsers.
Did you use a “remote” web based server-manager on this one?