For what it's worth, my feeling is that internal and simultaneous (and presumably identical) failures causing this engine failure are almost impossible. I hope.
The initial report leaves some room for conjecture.
So I'm left with two lines of thought.
1. Either both engines had not failed or they were degraded to differing degrees.
2. Given what I suppose above about the chances of an internal and simultaneous failure, I'm led towards thinking the cause was external or environmental.
Again, just a hunch but I believe the stage of flight may prove to be a factor. It may prove to be that the cause of this failure could not have been possible in the cruise.
FWIW I'm going with ice, thermal shock or something temperature related. But I feel that the fact that they were on an approach may be important.