I would suggest you to update the BIOS and then uninstall and reinstall the Wireless card driver on the system. Please enter your service tag # on the link below, select the OS and then download the BIOS from BIOS section and then wireless card driver from Network section onto the Desktop screen.

http://dell.to/18r60nI

Please follow the steps mentioned below to uninstall the wireless card.

1. Open the charms bar by moving the mouse to right top corner of the screen and inthe search box, Start typing devmgmt.msc and then press enter.
2. Select the wireless card and Bluetooth device under Network Adapter and right click on it
3. Now select properties.
4. In the properties window, under Driver tab, click on Uninstall button.
5. Check “Delete the driver software for this device.”
6. You want to delete the driver click OK.

After the uninstall finishes restart the system and install the drivers by using the file downloaded on the desktop screen.

I am having the exact same issue but with the WD-15 Dock. Dell have sent an engineer out to me to replace the motherboard, believing that to be the issue, however it is still happening. Do you believe that the above solution will work for me too?

There is an issue with the "idle power saving" setting on the realtek lan driver.

Check if this can help fix your issue :

• Launch device manager
• Open the concerned lan card (double click) which shall be named as "Realtek USB FE Family Controller" or approaching
• Go to advanced tab
• Set "Idle Power Saving" to off (deactivated) and validate

You will also note that the drive has "green internet" saving parameters, but they seems to work fine as least on my setup (Latitude 7520)

"Laptop has internet connection through the LAN cable connected to docking station"

Test the Laptop RJ-45 Ethernet when plugged directly into the modem/router. Does it have the same issue? If no, the fault is the docking station. If yes, the fault is the Laptop.

Where I work I have two laptops with docking stations with this same issue.  I will apply this fix and reply again with there is any success. 

I believe you have done these already ?

Trying a different dock with affected machine. ?

Trying a different ethernet cable/router/switch ?

Whenever connection is dropped other devices connected to dock remain connected ? 

Than it's most likely a Bad Motherboard (Type c/TB port). error code 27/43 mostly caused by hardware error. 

Connect the ethernet directly to the ethernet port to test it's functionality. Call Dell for motherboard replacement. 

I can confirm that these setting changes fixed two issues at the company I work for.  

Definitely worth a shot.