Some points.
The Southern Ocean is full of debris because it has nothing to bump into. It can just go round and round.
The Northern route could have gone through some very soft or non existent air defences and primary radar. Myanmar. The Myanmar/Chinese border, Tibet, Natal, Bangladesh, Bhutan, Tajikistan, Kyrgyzstan.
Especially in the early hours of the morning at the weekend.
It is very difficult not to have rechargeable lithium cells on a flight. They are in everything these days.
Very many thousand of torches like this are flying right now in jiffy bags, for instance:
UltraFire 2000Lm CREE XM-L T6 LED Zoom Zoomable Flashlight Torch Light 5 Modes | eBay
UK defence planners have seen this and must now be making a very good case for a purchase of Boeing P-8s. It is a scandal that we don't have this resource.
T7 entered service in 1995 and nearly 1,200 have been built, so it has many millions of flying hours. But this does not mean that every possible fault in the aircraft has been found. As BA 38 and SU-GBP proved.