With the default /ipv6 firewall filters, LAN traffic is not going to forward through the router with-out adding your local prefix to the address list.
https://wiki.mikrotik.com/wiki/Manual:Securing_Your_Router#IPv6
If ipv6 dhcp-client is used you can request a prefix. This prefix is not going to work with the default firewall settings because the dhcp-client does not have the option to add the received prefix to the allowed address-list. This should be a pull down menu in the dhcp-client (Feature request).
I am asking the community for a sanity check.
The first part is to make sure we are not leaving any old prefixes in the allowed addres-list. After the address list is cleaned up, add the prefix assigned via dhcp to the address list with the time out also provided via dhcp.
/ipv6 dhcp-client
add add-default-route=yes interface=ether1 pool-name=v6 request=address,prefix script="/ipv6 firewall address-list remove [find comment=\"dhcp\"]\r\
\n/ipv6 firewall address-list add comment=dhcp list=allowed address=[:pick [/ipv6 dhcp-client get 0 prefix ] 0 [:find [/ipv6 dhcp-client get 0 prefix] \",\"]] \\\r\
\ntimeout=[:pick [/ipv6 dhcp-client get 0 prefix ] ([:find [/ipv6 dhcp-client get 0 prefix] \",\"] +2) 99]}"
Is there a better way?