Large packet drop with bridge interface

[Maurizio]

Hello everybody.

I have a pfsense virtual machine running on ESXI 5.5 hypervisor ( Intel  E5-2670 0 @ 2.60GHz, 8 GB RAM ). Traffic flow between a bridge BRIDGE0 connecting two interfaces, OPT1 and OPT2 in transparent mode (no IP associated).
I have large drop of packets when traffic is over 200 Mbits/s. Our messages are 172 bytes UDP packets.
Other strange thing is that increasing the number of vCPUs (actually is 3) nothing changes at all, and packet are dropped.
FW is only checking that packets are UDPl
I think someting is missing in my configuration, hope someone could help me.

Thank you in advance.
Maurizio