IPV6 routing issue

[saddamus]

Hello,
I'm facing problem on IPV6.
I have configured WAN interface with IPv6 only (static) and upstream GW
LAN side is also static IPV6 only.  Both are /64 prefix. Carrier is routing LAN network with static route over WAN interface address.
If I ping google from host connected on the lan side, packets are leaving and ACK comes back to WAN interface, but does not go further to the LAN side.
If i ping from router IP that belongs to LAN, selecting WAN as source, it goes to upstream GW creating loop instead of being routed over LAN interface.
Its not firewall issue, rules are fiine and no sign of blocking in firewall logs.
Moreover, if i check exposed services on LAN hosts from outside, traffic is reaching them, so problem seem to be only wth packets originated from LAN (everything send over upstream gw goes fine, but return ends up on WAN interface).
What do i miss ?