That was my first thought too. Clotting and mechanical shredding of red blood cells. These can be problems even over the span of a single operation where bypass is used.
The hemolysis must've been insane. I wonder why ECMO pumps aren't always mechanical baffles or a bulb to be easier on the blood. Just playing drums or a riding a motorcycle can lower your ferritin reserves from nuking RBCs in your hands and arms.