I will have a stab
there was a message at some stage this morning to expect delays into Syd due ATC manning.
UA got the message and said we don’t have fuel for that MAV.
I see your message and raise you a Mayday.
judging by the tracking of the Aircraft into Sydney, there wasn’t a life or death fuel shortage....at least you would hope there would be better tracking if there was.
if this is the case there are going to be a lot of please explains going on right about now.