Apart from the fact I dont really know the answer specifically, I do know that it doesnt save everything, and it usually deletes from the earlier events , except in the case of onslaughts, and the lower ones dont appear to be onslaughts.

I can see the reason for the wavy yellow line,but the fact that there is a time difference,as far as I can tell,doesnt prove that any battles are missing, only you, and possibly the technicians would know this.

It had occurred to me that it might be down to maintenance, but I wonder if its significant that the battles above and below the wavy highlight line are different kinds of battles,and this might be the explanation.I also notice the line splits battles from different players is this a factor?