The sudden plunge, without warning, then lurch upward of Singapore Airlines flight SQ321 from London to Singapore is curious.

It's described as turbulence, probably was, but there are some weird things about it. From the little i've read, 'the experts' say that kind of turbulence coming out of nowhere is very unlikely, but theoretically possible. (bit like the pangolin-bat love-child)

Makes me countenance a possible cyber-attack. Did the plane drop coz the controls had been hacked, or the AI auto-pilot system simply malfunctioned?

The passengers were mainly from Aus (56) & UK (47)

It happened over Myanmar's Irrawaddy Basin - which is near the equator, so it would be turbulent - but it's also a good place to stage an attack. Handy to China.
Likely as described - a freak turbulence event - but actual details from the airline have been limited. Still not sure if there was a storm - or it was so-called 'clear air' turbulence. Seems the seat-belt signs were not on.

Sounds like something out of disaster movie according to the witnesses - people flying up & hitting the roof then falling awkwardly back on the seats.