Battery SOC gone 'odd'

System is only 4 days old, Hybrid 5kW, Battery 9.5kW and 6kWp of panels.
Yesterday will dull, and the battery only got up to ₅₅% charged before the evening, and was drawn down to 13% this morning.
It started to change with the morning light, and then at 09:30 having taken 1.5kW, the SOC shot up to 100% with a BMS over voltage, and is now hanging around the 80-90% mark with little charges and discharges.
I'm assuming this is wrong, and the 13% this morning would have been about right.....
I do have 1 cell which seems to be under volt on draw, and over volt on charge.

Cell 13 being the lead voltage wise in both charge and discharge points to a faulty cell to my eye. Should all run pretty much the same so (given the number of cycles) I'd imagine this is a straight RMA and replacement of the entire battery as its clearly faulty from factory.

Yes, looks to have failed now :-(