I believe your observations of range/state of charge fluctuations along with the LEAF Spy screenshots are consistent with the one weak cell pair. I had a couple of weak cell-pairs showing up in my 2015 before I traded it in on the 2019 so I am familiar with the sudden drop in range/SOC. I never had the SOC bars increase while driving because there were always 12 showing after a full charge. As someone already posted, each module has 4 cells inside--two cells in parallel are considered a cell-pair and then two cell-pairs are connected in series. The three terminals provide a way to measure the voltage of each cell-pair since the center terminal is the center point of the series string. You should read about 4 volts from either end terminal to the center terminal and 8 volts between the end terminals.
You are correct that the 2011 and 2012 battery packs from Japan are easier to open because the case is bolted together with a reusable gasket. You can either buy the factory service manual or purchase an online subscription at https://www.nissan-techinfo.com/Home.aspx so that you have ready access to the necessary service instructions.
You are correct that the 2011 and 2012 battery packs from Japan are easier to open because the case is bolted together with a reusable gasket. You can either buy the factory service manual or purchase an online subscription at https://www.nissan-techinfo.com/Home.aspx so that you have ready access to the necessary service instructions.