Do you to have IPv6 connectivity? If yes, then you need to fix that issue.
Does your provider gives you proper IPv6 connectivity? Do you know if they use Prefix Delegation? And if yes, what subnet size?
In my case Deutsche Telekom gives me /56 and the wan6 config is as simple as:
config interface 'wan6'
option device 'eth0.7' # You may need to adjust the device
option proto 'dhcpv6'
option reqaddress 'try'
option reqprefix '56'