Surface Pro 3 and Type Cover connection lost solution
Fix for an issue with the Surface Pro 3 and the Type Cover 3
This is a possible solution for when your Surface Pro 3 and the connected Type Cover can't seem to find each other;
It helps in the case when the keyboard's keys don't light up when you connect it to the Surface; neither in Windows nor in the Surface's configuration menu (accessible by holding Volume-Up and the start button on cold boot) and you see that in Windows's Device Manager the "Surface Type Cover Filter Device" under "keyboards" does not show up as it is being hidden since Windows thinks it's disconnected.
Try holding down the Power button and the Volume up button for 15 seconds. Then, wait a few seconds, and tap the Power button again. [Note: you only have to tap the power button to turn it on, don't hold it down] Plug the Surface Pro 3 into the charger.
Took me a couple of hours to find this information so I hope someone else might find this fix quicker as the help page on Microsoft's Type Cover support page does not clearly state this action as a potential fix for the issue.