Libtins Sender does not send all packets from Sniffer

I'm using libtins and i want to create a sniffer, that sends every packet received on eth1 to eth2:

bool callback(PDU &pdu) 
{
PacketSender sender("eth2"); 
sender.send(pdu); 
return true;
}

int main() 
{ 
SnifferConfiguration config;
config.set_immediate_mode(true);
config.set_promisc_mode(true);
config.set_direction(PCAP_D_IN);

Sniffer s1("eth1", config); 
s1.sniff_loop(callback);
}

The Sniffer works, but it does not send all packets to eth2. I#m sending ipv6 UDP Packets and SOME/IP Packets. Some of them are sent to eth2, some are not. But no no pattern recognizable. Can you help me to fix this?