It might be better to have a look at the Open Vehicle Monitoring System (OVMS). It supports the Leaf with a modern modem (Most TCUs are 2g, some were upgraded to 3g in places where 2g was shut down) and doesn't require the Nissan-specific stuff. This isn't really relevant to this thread, though.
If the error can't be cleared, it's likely a real error. The P3180 code is just a generic code that seems to be logged when the battery has any error - which is your P33D4, marking a high Hx.
@safetyuggs do you know the date of your in-car BMS' update and its firmware at the time you were able to get the SOH update to 'stick'? Were the ones on-bench able to 'stick'? I know mine, which had an update in 2016, had the Hx and SOH reset to 4 bars as well. Could it be an update Nissan put out that does anti-reset functions? It could certainly be a watchdog within another module in response to some kind of fear that people would reset SOH and sell lemons?