You didn't mention what charger you're using. The 4 button variety have problems sometimes where they essentially get stuck on the very final balance phase. It will be down to .1 amp and sit there for 10 or 20 mins. You'll see individual cells going up and down in voltage.

My suspicion is an over correction problem. The overall charge current is very low, the charger puts a discharge current on a cell and it overshoots bringing the cell down .02v instead of .01v.