The biggest problem with the Leaf's BMS (in my opinion) is the use of the Hall-effect current sensor. These are not very accurate for coulomb counting and subject to accuracy degrading effects, such as centerline drift, effects of the earths magnetic field, temperature, etc. The inaccuracy of this is why "some gids are more equal than others". Nissan compensates for this inaccuracy by applying corrections to the SoC by sampling voltage and using it formulas that also take into account the temperature, internal resistance, aging, etc. This is why you can gain/lose SoC suddenly sometimes after power cycling. It will apply changes all at once if the car is power cycled, but if in use, it will apply a correction in the form of a drift which appears as faster/slower SoC counting than real energy out/in.
I was able to meet with the Nissan engineers from Japan last December, including the battery system engineer (I had a one-on-one with him). Their explanation for why we have no direct SoC display in the car was basically that they were afraid to show it and have these corrections occasionally make it "jump" which would "confuse the customer". The Battery Systems Engineer told me that cost was the reason they used the Hall-Effect current counter rather than a more-accurate galvanic shunt.
It's looking like there is some degradation in these hot-climate packs, but it appears that the BMS (LBC) is not dealing with it properly, and not only indicating incorrect loss figures, but also possibly not allowing for full use (charging) of the packs real capacity.
Keep in mind, Nissan did a lot of testing, but the bulk of it is accelerated life tests, which attempt to simulate a much longer real-world use scenario. Unfortunately sometimes there is no substitute for real-world life testing, and it sounds like there are some unexpected results that the BMS software is not equipped to deal with.
Also remember that large automakers, especially Japanese ones, are very methodical about changing things, and it takes a long time to properly implement a fix. If that fix involves software in a critical system, (the LBC for example) it will take many hours of testing before they will even consider releasing it. I believe they will fix this, but it will be done on their terms which means it will take some time before we see a solution.
-Phil