IPv6 route advertisements are not received on the private interface

I’m trying a very simple setup where two nodes in my VPC have IPv6 enabled and a working radvd which assigns ULAs to eth1 (e.g. fdaa::/64 and advertises them. Both have the following /etc/radvd.conf:

interface eth1
{
        AdvSendAdvert on;
        MinRtrAdvInterval 30;
        MaxRtrAdvInterval 100;
        AdvDefaultLifetime 0;
        prefix fdaa::/64 {
        };
};

I can confirm that advertisements are send to ff02::1 but they are not received on the other machine. So, pinging one node from another using the assigned ULAs does not work. What is the problem?