Battery discharged itself to 3% - help/advice

[ApronCricket]

I noticed whilst checking through my history that my battery discharged itself to 3% just as it was supposed to stop discharging. I thought it may have been a bug in my recording, as I've jut moved away from the modbus HACS integration to my own modbus Node-Red data retrieval, but it is also recorded in the Fox Cloud data (just missed the 3% dip due to the 5minute resolution).

My On-Grid reserve was set at 16% with off grid reserve at 10%. No force charge/discharge profiles etc. I understand this is a perfectly safe/normal setting to have?

It seems that just as the battery was reaching 16% and should have stopped discharging, the discharge rate went from -1.8kW to -3.7kW and dropped from 16% to 13%, then 3% within a few minutes before starting the recovery charge at 900w.

I emailed Fox support, but haven't had anything back, so I was wondering if anyone can advise me on what to do/check.
From what I've read, this is very bad (potentially fatal) for the health of my battery!

In case it is relevant, I recently had the inverter upgraded to:
Master: 1.39
Slave: 1.01
Arm: 1.35

I have a KH10 inverter, 15kW PV total across 4 strings and 1x master, 2x slave ECS2900 batteries.

[Dave Foster]

It sounds as if your battery pack isn’t perfectly balanced yet, that usually manifests itself in jumps or drops of SoC.
The most important thing to say is that it won’t be damaged the BMS makes sure of that - but it might take a few charge cycles from empty to full and back again to balance properly and it’s usually recommended to charge from grid at this time of year when solar isn’t enough to fully charge them every month.