Better start off with a disclaimer: what follows is just half-informed speculation..
There's been some discussion recently in other subforums about the "pre charge" resistor, which is apparently used to limit the current that the main traction battery supplies to the motor drive electronics immediately after turn-on. Apparently, there's appreciable capacitance in those electronics, and closing the main contactor from the battery into that capacitance, if the capacitance was discharged, would result in a huge current spike. So the "pre-charge" relay is closed first, presenting a path from the battery into the capacitance that has enough series resistance to keep the initial current spike within reason. The other discussions speak of the power rating of that resistor being much too low to handle the charging current's level on a continuous basis; it only survives because the charging current pulse is brief. Well, if something were to invalidate the assumptions that the resistor selection depended on, it might easily burn out. And after it burns out, if its construction is of the type to fail open-circuit (like a fuse), then it would only emit a burning smell while it was burning out, and not after. And after it DID burn out, the car might still appear to work, if its main contactor is tough enough to handle the massive current surges for awhile. But you wouldn't want to ask it to do that very many times. Hopefully, the system's design includes the ability to verify that the drive electronics are successfully charged up before the main contactor can be ordered to close, so all this is probably unlikely.
Plenty of other possible scenarios for a temporary bad smell, though. For example, I understand that the newer LEAF models use a direct-to-air electrical heating element in their heating systems; those can get hot enough to burn debris that comes in contact with them. If the debris is small enough, it'll stop smoking after it finishes scorching. But that presumes that the heater was run at the time the smells were noticed.
Just some idle speculation.