I've been through all this as well. I gave up and spent a couple hundred dollars on an ALogic dual-thunderbolt connection dock. Two wires, not one, but perfect

I've been through all this as well. I gave up and spent a couple hundred dollars on an ALogic dual-thunderbolt connection dock. Two wires, not one, but perfect for my MacBook. It's been flawless, even after a year (most of the cheap docks I used died after 6 months). From what others I've spoken to, and myself have worked out, the only "solution" is to spend hundreds of dollars on the high end ones. They seem to be far more reliable (and have better support if something does go wrong). CalDigit is what most have moved to. My ALogic one is still kicking, so I'll stick with it for now.