This was a single channel automatic approach with a manual go around. The autopilot disconnected just at it should do. FZ SOP.
The MAK intitially report referenced made clear the approach was being manually flown. What is not so clear is:
1. Was the autothrottle engaged?
2. If thrust was being managed manually was the autothrottle ARM mode used?
3. Was a normal go-around flown or was it a Windshear escape manoeuvre?
There are many unanswered questions of "what" before we get into "why"
However, as many have already suggested, fatigued people may do strange things or end up behind the aircraft. I'm sure we have all done daft things in more benign conditions and been saved by altitude, reacquiring situational awareness, or the person in the other seat.
I have also operated while fatigued (not in an aircraft and during time in the military) and the ability to make basic mistakes in that condition is quite shocking.
On a regulatory front, I hope this will at the very least bring to the end the farce that the head of the Emirati regulatory body also happens to own EK and FZ...