" Certain types of engine icing might lead to an unresponsive engine, and this could affect both simultaneously; or with decreased efficiency on one, the other engine struggles which might make it more susceptible to the effects of ice, so shortly after both are affected.
Although most engines are anti-iced, some of the big fans rely on fan-ice shedding (centrifugal action) at higher rpm. "
I don't see anyone other than you suggesting that the engines themselves were 'iced up' !