When i find the forward issues with the firewall, will update the post.
Edit:
In the end had to edit /etc/config/firewall:
config rule
option target 'ACCEPT'
option name 'Allow-GuestWIFI-IPv6'
option family 'ipv6'
option proto 'icmp'
list icmp_type 'router-solicitation'
list icmp_type 'neighbour-solicitation'
list icmp_type 'router-advertisement'
list icmp_type 'neighbour-advertisement'
list icmp_type 'echo-request'
option src 'guestzone'
option src_ip 'fe80::/10