Finally got everything working properly, and had a bit of sun so that the battery charged up.
During the charging, at a rate up to 90 amps, ( btw the battery is 3P8S, total 840AH), the cell voltages kept close together; the display showed the BMS balancing doing its thing.
Then, as 100% is approached, cell 8 sort of accelerates and reaches the 3.55V charger cutoff. Over the last 10 minutes before the charger is shut off, the dV rises from less then 50 mV to 200. 10 minutes after the charger is shut off, the dV is back under 25mV.
There has only been two full charges so far, so I am not sure whether or not to be concerned about this.
A snapshot of the data is below, with the highest voltage cell highlighted.
Up to the few minutes shown below, the highest voltage cell is more or less evenly distributed among the 8, on a minute interval.
I have measured the resistance and the dV from each busbar to the battery terminal, and they are pretty consistent, and low. Prior to assembly, the cell IR's measured consistent within 0.03 milliohm.
I have the charge controller set at 29 volts, and it is under control of the SBMSO, so no absorb or float.
Has anyone seen a similar characteristic?