I'm part of the TCU Vampire club too.
Here is the behavior I observe:
1) The first indication that the TCU has gone into Vampire mode is getting the Yellow Triangle and there is no ability to get updates from the Leaf via the app or getting plug-in reminders.
2) I open up Leaf Spy Pro to check the codes and sure enough I'll have a somewhere from 1-8 codes, but the one that is ALWAYS there is P3131 EV.HEV System Shutoff Timeout.
3) Pulling the TCU Fuse for 30 seconds seems to do nothing to change the behavior
4) The next overnight in the garage, the battery will be flat dead (< 10VDC)
My (band-aid) solution:
Pull the negative battery cable for at least 15 minutes. Generally I pull of the cable overnight and put it on the BatteryMinder to put a full charge on it.
This seems to reset or reboot something in the car including the clearing the DTCs. The TCU will behave itself for the next 2 weeks - 3 months.
Why is this different? No idea.
Why does it start screwing up in the first place? No Idea.
Why doesn't it happen all the time? No idea.
Sorry, all I know is what seems to kick the TCU back into non-Vampire mode.
What I do know is I am a little OCD about monitoring my car with LSP and I know the battery is not just slowly draining over time until it's too weak to sustain the overnight Vampire treatment. I have left it in the garage for 2 weeks plugged into the EVSE and everything was fine. When I did replace the battery at the 3 year mark following a Vampire mode round, I drove it for a week, went on vacation for a week with it plugged into the EVSE, drove it for a week when I got back, and on the following Saturday it went into Vampire mode with the yellow triangle. It never killed the battery because I did the disconnect and everything has been peachy for the last 3 weeks.
While in Vampire mode I've tried a couple tests. I have tested in by charging the 12v in place in the car to full capacity during the day and overnight it will kill it again. If I pull (and leave out the TCU fuse) it won't. If I put the fuse back in, dead overnight again.
Just my $.02. Hope that helps some of you dealing with this on a multi-time a week basis.
P.S.
Nissan is really screwing the pooch on dealing with this. I've finally got my dealer trained to not deny there is a problem when I talk to them, but I know they are still denying the problem to others. I fear that Nissan will never fix the problem as if it was resolvable with a software patch they would have done it by now. That leaves it as a TCU replacement (again) and an expense they won't want to absorb. They'll deal with the complaints until they're all out of warranty or someone brings a class action.