Sorry Richard but your logic is flawed - unless the battery had full capacity, was discharged to 50%, and then suddenly lost half its capacity prior to recharge. In reality loss of capacity is gradual and so whatever is taken out on one cycle, giving whatever SoC reading (it doesn't matter) has to be put back on recharge plus 5% or whatever. Of course the actual SoC prior to recharge won't match the indicated SoC, but that is not the issue in this context.
Yes I was waiting for you to find the the flaw in my argument
Nevertheless based on use of two BMV600's I do find that you get such issues if the actual and programmed battery capacity are not at least roughly similar. Indeed I use it as a sign that I need to reset programmed capacity as batteries age. This issue is exaggerated if the BMV is not regularly synchronised by having it reach 100% SOC indication.