hoggy Agree, but ... the actual capacity hasn't been lost forever; it's just the BMS getting confused and doing what it thinks is the right thing. A calibration does (recalibrate it) put it back on an even keel but only for so long.
Our batteries charge fully every day (currently) and discharge to 50-60% overnight before PV starts to charge again. I haven't actually picked over the details yet but suspect that the voltage at which it reaches 100% will be dropping slightly each day.
When I'm back home in micro-manage mode, I think I'll be stopping charge on one battery each few days to allow it to discharge fully, then charge up again next day; leave things for a couple of days then discharge the other battery and monitor battery cell voltages to see if that has any discernible affect on capacity. We have had two sudden drops since the installation in January but wonder if that's simply because ours don't discharge very much below "60%" each day.