As I posted in the other thread - they generated graphs of the reports on Reddit and while there is a high correlation with ASRock boards it is far from only happening on ASRock boards, there does seem to be a high correlation with batch numbers and/or purchase date but that may be skewed by purchasing in the release window, etc. but it is not entirely confined to older purchases, the BIOS version has some implication but the problems appear to be far from isolated to being purely related to older ASRock BIOSes.
Most likely explanation so far is an edge case manufacturing issue which can be exacerbated by more than one condition.
Currently 9800X3D return rates are well under 1% with most retailers only seeing about half their returns being consistent with this failure - one retailer has reported 0.2% failures with over 20,000 units of the CPU sold.