Same problem here. I have an RB600 with a GigE device connected to it. Out of the blue this morning, the port locked up. It showed a few Kbps of TX traffic, but 0Kbps RX. A reboot caused the locked port to work OK, but then one of the other ports locked up in the same manner. After a couple more reboots, all ports were working fine.
This has to be a software issue....
We had this happen when we installed our first RB600 a couple months back. I though it was the device that was plugged into it, so I replaced that device and didn't have any problems until today.
I'm running ROS 3.15 with hardware firmware 2.18. I will be upgrading to ROS 3.16 tonight to see if that helps.
I've heard of interfaces flat out disappearing on the RB600s, and some people recommend downgrading the firmware to 2.16 to fix that. I'm not sure I want to try that, as it seems to be a different problem altogether.