mark exclamation,
I don't know if there's really a new twist.
Core icing in high-bypass turbofan engines has lately been the subject of some discussion, such as this
PPRuNe thread, discussing a Wall Street Journal article, as well as a small article in the German Spiegel weekly magazine. But what I've read, the symptoms are usually flameouts, almost always with a quick relight.
From what I gather one of the problems is that core-icing at cruise altitudes has for a long time been thought impossible, but has recently been established as a likely cause for flameouts at altitude. The icing is apparently caused by very small ice particles and/or supercooled droplets.
This
video mentions that drops above a certain size are normally deflected outward by the fan blades and do not enter the engine core. The very small size of the droplets/crystals in question may facilitate their entering the compressor and accumulating there under certain conditions, which, as of now, seem to be unknown. When larger chunks of that ice break free they may melt in the combustion chamber (or the later, hotter compressor stages) and cause a flameout, or even damage turbine blades.
Another thing that's peculiar about this form of ice accretion in the engine is that it may happen in conditions, under which the airframe does not suffer from ice accumulation.
To get back to the topic, in the case of BA038 there was no flameout, but "only" a failure to sustain a higher than "somewhat above flight idle" thrust. I'm still uncertain if there may be a connection. It seems unlikely, but then again, so does every possible explanation so far.
Bernd