I have a Dell WD22TB4 Thunderbolt dock that is connected to a Precision 3470 Laptop. I have had the laptop/dock combo since December and have had no issues until now. 

Last week the dock randomly loses its connection to the laptop. My monitors go into sleep mode and the light on the thunderbolt USB cable goes out (the light on the power cable brick stays on) . I have to disconnect the power supply from the dock and reconnect it and then the monitors etc. come back on. I have gone hours and even whole days without this occurring but once it does begin it happen it will do it literally every couple of minutes. 

I've tried restarting my laptop and had it disconnect almost immediately. I tried a full shutdown and restart and again within minutes it disconnects.

I thought maybe it was an issue with the USB port on the laptop and tried plugging the cable to a different port but that did not fix the issue.

I also tried plugging the docking station power supply into an entirely different power outlet but that had no impact.

What I have found is that if I shutdown my laptop at the end of the workday that when I start it back up the next morning is that I can go several hours before it starts disconnecting and a couple of occasions where I make through the entire day.

Anyone have any idea what's happening? Do I have a defective dock or is it an issue with the laptop? The dock seems to be behaving as if the laptop has been disconnect or powered downs (although the usb Thunderbolt cable light should still be on).