It could be because, as you described, you have taken the test before the insulin you have taken had ran out completely.........although you are on small amounts so your insulin may well have ran out before the 2.5 hours..........Apidra I think has a shorter duration than Novorapids 4.5 hours.......1-2.5 hours I believe.....
So it might be more likely that your Lantus dose, again small, has ran out by the time the night has come.........so you could try giving your Lantus in the morning to see what affect it has on the evening results....
I think you should also try targeting specific times when you are higher at night though as there could be many reasons for being high including food, illness, alcohol etc....