This suggests a couple things. First, a machining issue, where stress is allowed to focus at the tooling insult. This could also lead to susceptibility to degradation via corrosion, and failure. The problem is that corrosion that happens so quickly seems unusual.
And,
As with the RRTRENT spline AD, the possible link of coupling issues with powerful vibration and consequent failure of downstream internals is present with the GE.
The underlying issue may be a flirtation with minimum materials, both dimensionally, and inadvertently, in spec, and unproven economics.
I think these observations are conjecture without any data to support them, whatsoever.
The fan midshaft cracking and fracturing incidents on the Boeing 787 (GEnx-1B) were traced last month to a new, lead-free coating that allowed the component to corrode rapidly under certain conditions. GE switched to a leaded coating already used on the GE90 to correct the problem.
The problem on the 747-8F (GEnx-2B) has been traced to the Stage 1 LPT nozzle assembly problem which permitted one or more of the nozzle segments to shift aft contacting the Stage 1 LPT blade rotor during the early stage of TO.
The GEnx-1B engine used on the Boeing 787-8/-9 is 184.7" long and consists of 1 Fan, a 4 stage LPC, a 10 stage HPC, a 2 stage HPT, and a 7 stage LPT.
The GEnx-2B engine used on the 747-8F and 747-8 Intercontinental is 169.7" long, and consists of 1 fan, a 3 stage LPC, a 10 stage HPC, a 2 stage HPT, and a 6 stage LPT.
The HPC and HPT are common to both engines. The fan diameter is ~7.0" larger on the GEnx-1B verses the GEnx-2B. On both engines, the fan, LPC and LPT rotate counterclockwise relative to the HPC and HPT.