I've found a strange behavior of NICs on our server.
Server board: supermicro x9scl-f, OS: Windows Server 2012
NIC1=82574l - for LAN connections
NIC2=82579lm - for WAN connection (PPPoE)
Situation1. NIC1 and NIC2 set link speed to auto negotiation. Speed sets to 100M Full Duplex (its ok), but when copying large files from/to server (through NIC1), NIC2 hangs (can't access the gateway). Only system reboot helps.
Situation2. NIC1 and NIC2 set link speed to 100M Full Duplex. NIC2 works ok, NIC1 - file copying speed is very low (peeks at 10Mbit, sometimes simply freezes).