The native IPv6 address can not be aquired for K2(PS1218) frimvare

I find tha my router can't get the IPv6 adrress porperly .there some question about the LEDE

You will get no sensible answers, as you provided no details about your device, possible modems etc., network config and ISP's IPv6 support. Prefix delegation or not? Some 6rd config?

I use the default configure ,sometimes wan6 can get the ipv6 adrees, but after the router reboot wan6 can't.when I use the openwrt everthing is ok . I a sudent from chinese.