Well here's a potentially new twist, as I haven't read all the posts maybe it's been mentioned B4.
Mate of mine who flys the 777 made the same arrival into Heathrow from LAM a couple of hours B4 the stricken A/C. Now, aficionados correct me if I'm wrong, the 777 has both auto engine A/ice and auto Airframe A/ice systems. My mate had obviously seen operation of the engine a\ice system many times but never the auto airframe a\ice. That morning, apparently, the icing in the LAM hold was so severe that for the first time that he had seen the auto airframe a\ice system operated. He was so surprised that the fact was mentioned to ATC and later the ATIS was updated to mention severe icing.
He also mentioned that those huge Trents can have a problem with ''core icing'' but didn't elucidate on the matter!
Could severe icing during potentially a textbook CDA approach from the hold with the throttles almost closed right down to 600' produce a lack of response from the Trents as seen on the BA A/C?
I commend this question to the house!
Take care