From experience observing complex fluids in experimental systems, I believe cold fuel in the lines leading to the pumps might have a tendency to 'shear' and locally develop some very abnormal physical properties if the supply flow is disrupted upstream and the downstream pumps are still doing their best to push max fuel toward the engines.
Any gasses dissolved in the fuel would increase in volume and come out of solution. Some volatile fractions of the fuel itself might gassify. Whipped around by the under-loaded and possibly over-heating pump impeller blades, the gas plus liquid would flow forward as a frothy foam, still burn-capable but much lower in density and fuel energy than normal.