If so, fatigue would almost certainly be a factor, (which, of course, would have to be investigated just like all other possibilities and explanations).
Fatigue may well have played a part. This
appears to the chronology of events for the aircraft and crew that day from a reliable source.
The aircraft originated from Palu (PLW) in central Sulawesi with a scheduled departure time of 0605 so "sign on" time for the crew would have been 0505. The first sector was to Balikpapan (BPN) in Kalimantan, followed by Banjarmasin (BDJ), before heading to Bandung (BDO). In Bandung, the scheduled departure time for Denpasar was 1020, however, that day, Lion combined all three flights from Bandung to Denpasar in to one, that being JT 904 departing Bandung at 1200 with a scheduled arrival time at Denpasar of 1445.
The time that the aircraft impacted the water was reported to be 1510, which meant that the crew had been on duty for 10 hours when the accident occurred. Although this in itself is still well within the legal daily limits, you would still need to consider and analyze the flight and duty times of the crew prior to the accident to see if adequate rest had infact been given to the crew.