When no hostname is defined in /etc/hostname and NetworkManager does reverse DNS address lookup to obtain the hostname, it appears fail with IPv6 while it works successfully with IPv4.

This is with release 4.12
$ rpm -qa | grep Network
NetworkManager-libnm-1.36.0-11.el8_6.x86_64
NetworkManager-ovs-1.36.0-11.el8_6.x86_64
NetworkManager-1.36.0-11.el8_6.x86_64
NetworkManager-team-1.36.0-11.el8_6.x86_64
NetworkManager-cloud-setup-1.36.0-11.el8_6.x86_64
NetworkManager-tui-1.36.0-11.el8_6.x86_64

I can provide access to a system that always duplicates the failure or get the full journal logs, this is the relevant piece of the journal
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:1 'hostname': completed (6 scripts)
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname': start running ordered scripts...
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/usr/lib/NetworkManager/dispatcher.d/04-iscsi": run script
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/usr/lib/NetworkManager/dispatcher.d/04-iscsi": complete
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-chrony-dhcp": run script
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-chrony-dhcp": complete
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-chrony-onoffline": run script
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-chrony-onoffline": complete
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-coreos-chrony-dhcp": run script
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/20-coreos-chrony-dhcp": complete
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/90-console-login-helper-messages-gensnippet_if": run script
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname', "/etc/NetworkManager/dispatcher.d/90-console-login-helper-messages-gensnippet_if": complete
Jan 31 13:57:30 localhost.localdomain nm-dispatcher[1574]: req:3 'hostname': completed (6 scripts)
Jan 31 13:57:40 localhost.localdomain NetworkManager[1492]: <debug> [1675173460.4973] resolve-addr[d5d01c4a29e36f3c,fd2e:6f44:5dd8:c956::50]: helper returned hostname '(null)'
Jan 31 13:57:40 localhost.localdomain NetworkManager[1492]: <debug> [1675173460.4973] device[cc347b902d3fc62f] (enp2s0): hostname-from-dns: lookup error for fd2e:6f44:5dd8:c956::50: helper process exited with status 3
Jan 31 13:58:00 localhost.localdomain systemd[1]: systemd-hostnamed.service: Succeeded.

The hostname is configured in an external dns and if I run at script at boot I'm able to get the hostname successfully, so I'm not sure why NM is failing to get it. This is the script I can use as a workaround:
   ips=$(hostname -I)
   while [[ $ips == "" ]]
   do
      echo "Waiting for IPs to appear for reverse DNS" 1>&2
      sleep 5
      ips=$(hostname -I)
   done   for ip in ${ips}
   do
      echo "Reverse dns for $ip" 1>&2
      hostname=$(dig -x $ip +short)
      # If hostname returned, configure it
      if [[ $hostname != "" ]]; then
         hostnamectl set-hostname "${hostname}"
         echo "Setting hostname to ${hostname}" 1>&2
      fi
   done

Every time

1. Using OCP agent based installer in dev-scripts setup
2. Run a test with IPv6 and hostname configured in DNS
3. 

Hostname does not get resolved and stays at "localhost"

Hostname gets set to the value in DNS