Plesk is not accessible via its hostname https://host.example.com:8443:
PLESK_INFO: This site can’t be reached
host.example.com took too long to respond.
Plesk is accessible via an IP address https://203.0.113.3:8443
Hostname is resolved to another IP address:
# nslookup example.com
This IP exists in Plesk > Tools & Settings > IP Addresses;
This IP address does not respond to external requests:
# ping 203.0.113.2
PING 203.0.113.2 (203.0.113.2) 56(84) bytes of data.
--- 203.0.113.2 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 13999ms
# nmap -Pn 203.0.113.2 -p8443,8880
PORT STATE SERVICE
8443/tcp filtered https-alt
8880/tcp filtered cddbp-alt
Network configuration issue. The IP address configured on the server is not accessible.
Review network configuration, or switch the hostname DNS zone to another valid IP address.