:log info "Start"
:foreach idx in=[/ip/firewall/address-list/find list=PRIORITY_HOSTS] do={
    :local ip [/ip/firewall/address-list/get $idx address];
    :local tag [/ip/firewall/address-list/get $idx comment];
    :local lease [/ip/dhcp-server/lease/find where address=$ip];
    :local mac [/ip/dhcp-server/lease/get $lease mac-address];

    :foreach n in=[/ipv6/neighbor/find where mac-address=$mac interface=BRIDGE_LAN] do={
        :local candidate [/ipv6/neighbor/get $n address]
        :log info [:serialize value=$candidate to=json]
        :if ([:len $candidate] > 0 && [:pick $candidate 0 4] = "2605") do={

            :log info ("/ipv6/firewall/address-list/print where list=PRIORITY_HOSTS address=" . $candidate);
            # ^^^ IF I RUN THIS COMMAND IT RETURNS A VALID MATCH

            :log info (":put [/ipv6/firewall/address-list/find list=PRIORITY_HOSTS address=" . $candidate . "]");
            # ^^^ IF I RUN THIS COMMAND IT RETURNS A VALID MATCH

            :local existing [/ipv6/firewall/address-list/find list=PRIORITY_HOSTS address=$candidate];
            # ^^^ NEVER POPULATED EVEN THOUGH LIST ENTRY IS 100% VERIFIED TO EXIST AND BOTH PRINT AND FIND COMMANDS 100% RETURN A MATCH MANUALLY

            :if ([:len $existing] = 0) do={
                /ipv6/firewall/address-list/add comment=$tag list=PRIORITY_HOSTS timeout=1:0:0 address=$candidate;
                # ^^^ ALWAYS THROWS ERROR BECAUSE ENTRY EXISTS
            } else={
                /ipv6/firewall/address-list/set $existing timeout=4:0:0;
                # ^^^ NEVER RUN BECAUSE `existing` IS NOT POPULATED
            }
        }
    }
}
:log info "End"