Are you able to draw actual voltage versus time curves? And post them here, that would be a lot easier to get an overview of.
If you have the equipment, you can test each cell individual in a stick pack. It's just a lot of hazzle...
So with curves, it might be easier to judge, if it's a problem worth concerning. If it's a problem, it might be worth to tear that stick pack apart.... And change the bad cell.
How do this particular pack perform on the track, compared to the others? Any noticable difference?
Are you allowed to run saddle packs? To my experience Sanyo responds really well on an equalizer.