The IPv6 address is not removed from the config store, where we persist the configuration of VMkernel NIC adapter. After ESXi host reboot, the IPv6 address is restored from config store.
This issue is fixed in VMware vSphere ESXi 7.0.3
configstorecli config current get -c esx -g network -k vmknics -outfile tmp.json
"ipv6_address": [
{
"address": "xxxx:x:xxx:xxxx::xx",
"prefix_length": 64
}
configstorecli config current set -c esx -g network -k vmknics -infile tmp.json