I am available for custom hardware/firmware development
I wouldn't use your 57 Ah figure to calculate the battery capacity. I would use the 66 Ah reading when the first cell reached 2.8V.
Do you believe all the cells have issues, or just some?
This is why I have an interest in the BMS24T BMS. It claims 1.2A of balancing.
It would be less confusing if cell 1 in the first cell logger was physically cell 1.
Your connections are all clean and low ohms?
Does your imbalance change with a high load vs no load?
What happens if you leave your cell logger completely disconnected and only use your voltmeter?
While charging, I'd use the volt meter to probe different positions on the bus bars and battery terminals. For example, terminal-to-terminal and then far end of bus bar on one terminal to far end of bus bar on other terminal.If you have low resistance connections and bus bars, then the voltage will be the same no matter where you measure.
You also have separate balancing circuitry connected? If so, it could cause imbalance and should also be disconnected for a test.
@LostinSpace How are things doing with your project you went silent.