Total flight time was 4hr 31m (18:17 UTC to 22:48 UTC)
Tracking suggests it maintained 17,000 ft altitude since 21:02 UTC (no tracking before that).
This being 12hr flight they either dumped or lost lot of fuel. FL suggests engine shutdown. Probably ignited on landing.
Fuel line rupture/failure inside the engine and fuel value failure(not able to shut off), may be.
Based on JACDEC track plot, BKK would be the closest major, but if they have to dump fuel SIN is not a bad option.
Assuming there is not much fuel left, I think it is too early to second guess crew's actions.