some weird problem with em network interface

Hello

I've been using a pcengines apu4 board for about 3 years now. I noticed a problem that I can't precisely undestand with the em network interfaces (Intel I211).
I'm using 2 interfaces in gigabit mode, one in 100 Mbps and another in 10 Mbps.
Intefaces in gigabit mode work very well. The other ones are intermitent. Sometimes works and suddenly stop working.
For instance, when I ping the interfaces (100 and 10 Mbps) from another computer connected to the network sometimes works and sometimes don't. When the problem occurs, the packets don't show up in tcpdump.

I connected another interface (axe0: AX88772) in USB port and configured it exactly the same as a 10 or 100 Mbps interface and it works perfectly, with no errors at all.

My question is: is there any known problem with the em driver ?

Thanks,
Paulo.