I think that for the GEnx-1B engine, a couple of fan related problems related to ice shedding and fan imbalance caused shutdowns. This problem was solved by having the engine power increased to 85% N1 periodically when cruising in potential icing conditions with N1 below 85%. Also, a PIP version of the engine produced for certain airlines closed down the fan blade to fan casing clearance, improving SFC. However, that resulted in ice shedding causing fan blade damage and the clearances had to be increased.