When you connect the dock does it directly connect to the Nvidia GPU or does the laptop have a mux that switches when the GPU is activated? I think Nvidia calls it advanced Optimus.maybe try forcing dGPU only in the bios and see if it still happens.
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Now solved: this was a power delivery issue where if the power draw for the machine got too high and the laptops dedicated power brick wasn't connected, the dock would try and fail to deliver the amount of power needed, trip over itself, and end up shutting down entirely instead of just not delivering as much power.
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