NAT64 with R80.40

[pal]

This is my first IPv6 implementation on Azure

Lab setup is 

Ext win10: fd5d:7ce8:b6d5:1::4 (10.20.1.6)

fw Ext (eth0): fd5d:7ce8:b6d5:1::a14:205 (10.20.1.4)
fw Int (eth1): fd5d:7ce8:b6d5:2::4 (10.20.2.4)

webs1: 10.20.2.5

My NAT64 rule is 

    

Log shows xlate dst as expected but xlate_src is empty

fw6 monitor and tcpdump on eth0 shows fw is sending reset

Any help is appreciated!