Stateless Ipv6 doesn't work in OpenWrt(LEDE)

Stateless Ipv6 seems can not work fine. I can get ipv6 address and get default gateway. But when I try to ping gateway. Only “network unreachable” is returned. And also can not ping another device under same switch.

I find a X86 rother which is work fine and try to catch some packages. But I can’t understand in my knowledge.

The “BPI-R2_wan6.pcap” and “X86Rother_wan6-fix.pcap” use command tcpdump -i $interface ip6 -vv -w $file before i plug in the cable. And stop when i see ipv6 address in Luci.
All pcap use filter icmpv6 and dhcpv6 in wireshark

In order to protect privacy. I use “FFFF:FFFF:FFFF:FFFC” to replace public address

BPI-R2_wan6.pcap (1.5 KB) (under another LEDE rother use Stateful Ipv6)
X86Rother_wan6-fix.pcap (1.5 KB) (in public network use Stateless Ipv6)
BPI-R2_wan6-PublicNetwork-fix.pcap (13.5 KB) (in public network use Stateless Ipv6. can’t get ipv6 address when i stop it)

Could any body analysis those packages? Or try this in your network.