If the Hetzner server was replaced which includes the network card or motherboard,but not the disks, you need to update the networking configuration and firewall to reflect the new interface name. Use the Hetzner rescue console and mount the partition e.g.
mount /dev/md2 /mnt
Update the interface name in /etc/network/interfaces
root@rescue /mnt # cat etc/network/interfaces ### Hetzner Online GmbH installimage source /etc/network/interfaces.d/* auto lo iface lo inet loopback iface lo inet6 loopback auto enp41s0 iface enp41s0 inet static address 157.90.212.174 netmask 255.255.255.192 gateway 157.90.212.129 # route 157.90.212.128/26 via 157.90.212.129 up route add -net 157.90.212.128 netmask 255.255.255.192 gw 157.90.212.129 dev enp41s0 iface enp41s0 inet6 static address 2a01:4f8:252:19d1::2 netmask 64 gateway fe80::1
Replace the enp41s0 with the new name, which you can get by running
udevadm test-builtin net_id /sys/class/net/eth0 | grep '^ID_NET_NAME_PATH'.
Don't forget the update firewall. In case of shorewall update the /etc/shorewall/interfaces file. Then reboot the server.