This is an install from scratch on two nodes. I can reprodice the issue, multiple times.
root@pve02:~# cat /etc/pve/sdn/zones.cfg
qinq: q4064
bridge vmbr0
tag 4064
ipam pve
vlan-protocol 802.1ad
root@pve02:~# cat /etc/pve/sdn/vnets.cfg
vnet: v4064
zone...