Occassionally the fan blade attrition liner starts to crack and disbond. The limits are far more restrictive than on the RB211 or 535 and requires a hangar input almost immediately for fan blades out and a new liner bonded in. Once a crack starts it usually gets worse very quickly (probably from all the vibration these engines seem to manufacture for themselves)
What seems to be a bigger problem is the acoustic lining in the c ducts. Once this debonds somewhere on the inner or outer barrels it normally comes off in big strips requiring a c duct change (hopefully after a ferry flight to the hangar). I have seen a few c ducts with just a perforated aluminum skin (aka 535 and other RB211's) which seems a definate improvement on the metallic fabric type.. presumably a mod on later aircraft?
The CFM drinks a lot more fuel and is a lot noisier but apart from the odd fan blade blend out and HMU change never really seems to go wrong.