Logitech wireless mouse not working with gigabit ethernet adapter plugged in? I am seeing baffling behavior with my wireless mouse (connected via USB) and my gigabit ethernet adapter plugged in simultaneously.

If my mouse is plugged in and working fine, if I plug in my gigabit ethernet adapter (even without the ethernet port plugged in) to EITHER thunderbolt port, my Logitech m510 mouse stops working completely.

I have plugged in my external monitor to both thunderbolt ports, and it doesn't affect my mouse at all. What the hell is going on here?
The reason you are seeing the symptoms present when you connect an ethernet adapter to the TB port and not when you connect a monitor to the TB port has to do with what is being passed over the TB cable.

TB multiplexes at least 2 signals over the same connection.  In this case, video and PCIe.  Yes, basically the same PCIe bus that you would find looking inside any computer is now on that cable.

Thunderbolt Technology Brief

So, basically speaking, when you are connecting the DP to TB, you only get video.  When you connect the ethernet adapter, you are connecting to PCIe.  When you daisy chain devices, you get both.

Your mouse stops working because the ethernet adapter is generating noise that is interfering with your receiver.  It is the PCIe "signals" that is creating this noise within the ethernet adapter.  It is not interfering with the USB port - just the wireless radio reception/transmission of the receiver.  I know this for a fact because:

1)  I experienced it myself. I have a Logitech Anywhere MX (non bluetooth) and bought a TB to Ethernet adapter.  I had the same issue.  I changed out my TB to Ethernet adapter to a more reputable brand and the problem went away.

2)  I found this answer on Logitech support forum

3)  Plug in a USB hard drive.  If it was interfering with the USB, the hard drive would fail as your mouse does.

The reason that when you move it from one port to another it "sorta" works is because you have lessened the wireless interference, not eliminated it.

Here is the Apple Ethernet adapter that I bought that solved my issue.  

If you want to confirm this, buy a USB extension cable to move your unifying receiver to another location (sometimes logitech includes this with their mouse).  Or, plug in the unifying receiver into a hub away from the ethernet adapter.  The problem should go away.