John47:
I wonder whether the problems they experienced may have started just after 1 h 35 min 43
It may be infered that communication problems started at this point because she didn't answered those three calls from Brazilian ATC. But her SATCOM worked fine until 0214 and nothing from the flight parameters published may imply that she had other trouble than communication ones until 0210. Beside, communication issues are usual and nobody worried seriously about it. Aircraft are routinely suffering radio problems mainly due to the ITCZ weather. Routine issues are killing awareness, then no alert was issued until very late.
S~
Olivier