Cell Balancing within a Battery Pack is one thing, Balancing between packs is another thing.
Cell balancing will only keep cells within a single pack closer together BUT no balancer can fix or compensate for poor/weak cells.
Passive Balancing only burns off Hi Volts from Hi Cells.
Active Balancing can transfer Hi Volts to Lo Volt cells within the same battery pack.
Packs will and do behave independently and some minor deviation between them is not unusual. Most often some of this can be attributed to the installation, every lug, fuse, terminal etc adds resistence and as such contribute to Voltage & Amperage drops.
NOTE !
Voltage Differential (OffSet) will always be different during Charge VS Discharge this is just the way it is.
Charger Devices (SCC, External Charger or Inverter/Charger (if used for charging) need to be corrected so they charge to the ACTUAL points desired on the battery packs, so that you do not over/undershoot.
DISCHARGE Devices like the Inverter (if not used for charging) must be corrected so that the Values are matched to the battery pack states during Discharge otherwise your 40,0V Cutoff (2,50Vpc) could be lower & causing damage.
FYI: LFP in series is not generally recommended and is more oriented to serve the "Drop-In Replacement" crowd more or less. There are several issues doing so. This is why the Standing Recommendation is to build & buy a Battery Pack assembly for your Target Voltage, be it 12,24,48 or higher.
ON BALANCERS, I have used many & tested several. They are NOT EQUAL and some are downright junk and others are very specific to the exact chemistry. I have used
QNBBM-8S Active Balancers on my 8S Packs and these do exactly as stated and quite well at that as well. BUT I am now changing my entire fleet of BMS' (production & utility packs) to
JKBMS' with 2A Active Balancers BlueTooth/CanBus/RS485. My current fleet includes 6x Chargery BMS8T with 300A Solid State Contactors and QNBBM Active Balancers, JK-BMS & JBD-Bms' with add-on HelTec Capacitive Balancers representing a couple of grand worth of gear to go into the used parts bin.