To me, the fuel pump should be able to override a vacuum in your tank.
But in theory, a vacuum in your tank would fight the flow of fuel out of the tank. The sand is a red herring. The low gas level creates a larger vapor space in the tank. The cold weather also creates a vacuum as the volume of the vapor space does not contract much to compensate for the decreased temperature and you can create a lower pressure system this way, because if the volume remains constant, then a decrease in temperature directly causes a decrease in pressure. These two things combined created a vacuum space in your tank (as compared to the outside air).
I still question though whether this should be able to fight against a fuel pump. They are designed to start the car under these conditions.
Bad fuel pump? Partially clogged fuel system could contribute to this? Anyone else have thoughts?