Yet another hypothesis
While no stone is being left unturned, here's another one:
Assuming that the cabin crew started heating food as soon as possible after takeoff, 25 minutes into the flight could conceivably be the time it takes for the food heaters to reach high temperature. One (or more) of those food packages could have been a bomb - disguised as a meal (breakfast?) – detonated by being heated to a moderately high temperature.
So obviously it would have happened in the rear galley, and powerful enough to knock out the rear section.