Although I never had the severe symptoms described in this thread, I found marginal 12V negative terminal to body ground connection issues on both 2011 and 2015 (no issues so far with 2019). There is a connection in the negative battery cable that looks like a cable clip, but is actually a connection for chassis ground (on left fender well near the 12V battery). On both cars, there was paint under the terminal and in the threads in the body which created high-resistance, marginal connection so there was some voltage difference between the case of the DC-DC converter and the body. Running the HVAC blower fan on high would increase the voltage difference and could cause the intermittent problems noted in this thread.
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015; traded 8/10/2019 at 82,436 miles
White LEAF 2019 SL Plus purchased 8/10/2019