I don't have any specific knowledge about the ANA issue (I don't work Trent and I don't work 787). But as Turbine D noted, all gas turbine issues are susceptible to hot section corrosion due to sulfur and other contaminants in the fuel and air - it's just a matter of degree. There are coatings that are used on the turbine blades to prevent corrosion - some work better than others.
Educated guess here, but I suspect ANA had a turbine blade failure or a borescope finding. When the looked into it they discovered a widespread problem had developed and they needed to take prompt corrective action.