So now we know, the cause was excessive rubbing of the 3rd stage fan blisk at the front end of the engine. This is certainly an unusual problem in that the diameter of a blisk can be carefully controlled during the machining operation. It will be interesting to learn of the corrective action, it might not be that the blisk is the problem, but the casing surrounding it.
Relative to the actual fan :
If the blades were hollow for the sake of cooling then that might mean that some other measure will have to be taken to prevent them from melting - with other undesirable trade-offs.
Fan blades are made hollow to save weight not for cooling purposes. Hollow fan blades are more expensive to produce, but weight savings is a huge driver. Think of the fan of the engine, the shaft which connects it to the low pressure turbine and the low pressure turbine, as a bar bell. The higher the weight of the fan rotor and the LPT rotor, the higher the pressure is on shaft to bend. The shaft bearings and the bearing structural supports keep shaft bending from happening. So increased weight of rotating components can result in additional weight being added to structural support components, a mushrooming situation.