RESOLVED

After reading Tom's config and adjusting mine this seems to be now working across reboots and I can restart netif without any issues now.

/etc/rc.conf

# WiFi
ifconfig_re1="up"
ifconfig_iwlwifi0="ether *:*:*:*:*:*"
wlans_iwlwifi0="wlan0"
ifconfig_wlan0="WPA"
cloned_interfaces="lagg0"
ifconfig_lagg0="up laggproto failover laggport re1 laggport wlan0 DHCP"
Thanks Tom ! 😉