@David-TP 

I've not tried swapping the units over but expect the behaviour to be exactly the same. This is the second PX50 twin pack I have owned. I sent the first units back and received a replacement for exactly the same behaviour as I described above, so I assume this is a common fault with the model.

The issue happens at least twice a week, usually in the evening when the laptop connected to the Dell dock is not being used (my work laptop would be turned off, but the Dock is still powered on).

Most of the time the unit is still displaying a green light, like it has a connection to the Main unit, but it will not supply an internet connection. The PC shows 'No Internet available' against the Ethernet connection connected to the unit. Occasionally it will show the red flashing lights like the unit does not have a connection to the main unit. A reboot can fix this and turn it green, but I still need to power up the laptop to force a reconnection of all the hard-wired devices on the satellite unit.

  @David-TP 

Could there be any consideration of the unit going into a power saving mode? I know Windows can tell hardware devices to power save to limit energy consumption (e.g. an Ethernet socket connection).

The Dell dock is always powered on, but the laptop connected to it isn't. Could the laptop being powered off tell the Dock it should be in a low power state and this translates to the PX50 as the Ethernet should also be in a sleep or low power state?

  @Bug_Boy 

I've seen that type of Ethernet issue reported with laptop dock before, but can't find the link. See if this can help:

In device manager all devices under USB controllers must have power management turned off (this was recommended by dell tech support).

* Make sure the dock is plugged into its AC power adapter
* Dock the laptop
* Once into Windows, open the Device Manager
* Expand Network adapters
* Look for the Ethernet connection (Realtek GBe Family Controller, or other Ethernet listing)
* Right click it, click Properties
* Click the Power Management tab
* Remove all checks
* Click the Advanced tab
* Change Selective Suspend to Disabled

  @Alexandre. 

Many thanks for this. I tried the options you mentioned, but I am still seeing issues after the edits.

@David-TP  the problem is 100% caused by the Dell docking station. Proved this over the weekend. I had my gaming PC running with the laptop turned off and disconnected. I plugged the dock into the disconnected laptop (to tidy my desk) and my gaming PC immediately lost internet and network connectivity on Ethernet. I unplugged the dock from the powered down laptop and my connection returned straight away.