em, pf - losing tcp traffic

[Marcin Gryszkalis]

Hi
I have pretty old gateway that started to behave strange.

Few times a day the lan interface stops receiving tcp and icmp traffic.
With tcpdump I can see arp, dns (udp), rtp over udp, netbios 
broadcasts (169.254/16), sip packets - but no tcp and also icmp ping 
replies 
stop coming.

The only way to fix it is ifconfig down + ifconfig up.

The system is 11.2(amd64).
Card:
em3 at pci0:7:0:0: class=0x020000 card=0x002e8086 chip=0x100e8086 rev=0x02 
hdr=0x00
    vendor     = 'Intel Corporation'
    device     = '82540EM Gigabit Ethernet Controller'

lan0: flags=8947<UP,BROADCAST,DEBUG,RUNNING,PROMISC,SIMPLEX,MULTICAST> 
metric 0 mtu 1500
        
options=209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC>
        ether 00:07:e9:11:24:61
        hwaddr 00:07:e9:11:24:61
        inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255 
        nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active

pf limits are not reached, pf reload or restart doesn't help.

The switch is dummy L2 so it shouldn't be able to recognize udp from tcp. 

I don't know what else could I check or try... 
Please advise :)

best regards
-- 
Marcin Gryszkalis, PGP 0xA5DBEEC7 http://fork.pl/gpg.txt