HF-sets
Excuse a comment from a non-aviator/ but one who directed safety related research in the nuclear field for may years before retiring:
I have been following this string for a long time now, and much of the reasoning is very interesting also in a broader context.
According the first interim report the aircraft had two HF-sets (Tx/Rx). One way both could be down is if their connection to the HF-antenna in the VS failed in some way. This could possibly hint at some emerging problem with the VS-connection to the main airframe (however this is a very long shot). I have been thinking about the accident with PartnAir long ago where some strange symptoms were seen earlier - but ignored.
Regards