My Wild Speculation
Basically everything working well: the radar and crew spot a wet cb and avoid it, perhaps even begin to think they have gotten through the ITCZ.
The radar and crew do not see a humongous dry/ice crystal updraft and fly into it. The temperature is so much warmer than standard that the a/c stalls somewhere in the updraft. Pitots may or may not be clogging while this is happening.
I am waiting for the BEA to learn how this or a different situation was handled by the crew.
Once both engines stall because because of high alpha, pulling one back to idle will not induce a roll.