I admit right up front that I do not know anything about the D3. However, I have a Jeti 130 that did exactly the same thing. The problem was the "low voltage" cutoff setting. I thought it was safe at 3.5 volts per cell, but it wasn't. I had mine set for a "soft" cut off so it just sagged a little and then came back just like your ESC is doing. I fixed the problem by lowering the cutoff voltage setting to 3.2 volts per cell.