There was apparently a letter from AirServices Australia to the ATSB which cited that on the day QF28 called a diversion to NTL there were only 3 ATC rather than the usual 5. The ATSB has since opened an investigation into the diversion of QF28. The diversion likely was the sentinel event but the various underlying issues such as effect of weather and ATC shortages would possibly also be investigated.
ATC shortages apparently have triggered a ground delay program at SYD on multiple occasions. I'm not sure what a "ground delay program" actually means but runway restrictions appear to be part of it. The idea is to reduce the arrival tempo - often significantly.
