Intel I210: Excessive Collisions on TX

Hi.

We've met some issue with I210 controller.
I210 is used in linux environment (MSI-X, multiqueue).

RX queues seems to be working (we can receive packets).

But we've found that each and every transmitted TX descriptor contains E1000_TXD_STAT_EC (i.e 0x00000002, Excess Collisions) bit in status field.

So, what are the possible reasons of "Excess Collision" on every TX packet?

Thanks in advance.