No IPv6 delegation on lan interface

Installing and Using OpenWrt
14

Try removing these:

/etc/config/network

config interface 'lan'
	option ip6hint '10'
	option delegate '0'

config interface 'wan'
	option delegate '0'

config interface 'wan6'
    option norelease '1'

/etc/config/dhcp

config dhcp 'lan'
	option ra_management '1'
	option ndp 'relay'

And add these (one of them replaces ra_management, which is deprecated):

config dhcp 'lan'
        list ra_flags 'managed-config'
        list ra_flags 'other-config'

Also, just because your ISP says it's working, doesn't mean you are not hitting a odhcp6c bug triggered by badly configured DHCPv6 servers, see: Odhcp6c issue with my ISP's configuration
I literally had to manually patch and recompile odhcp6c.