The apparent problem is hot corrosion caused by sulfur.
Sulfur in the fuel and airborne salts like sodium and chlorine reacts with the oxide layer on the blades in the high temperature environment of the turbine to attack the base metal of the blades. As a normal by-product of combustion, sulfur oxides are formed that combine with the salts and other elements ingested into the engine. This reaction forms sodium sulfates that expose the blade's protective oxide layer to decay. Water is also produced as a by-product of hydrocarbon fuel combustion, and this water can combine with the sodium sulfur compounds to produce sulfuric acid.
Usually, the attack is worse in the blade shank or tip shroud areas and the actual gas path airfoil area looks pretty good. Because of this, blades have to be removed from the rotor disk to determine if cracks are present. And that is what ANA will do on all their RR engines. There are coatings that can be applied to mitigate hot corrosion. All jet engines including turboprop engines can have this problem to a degree.