Hey guys, chiming in here with a third account of this problem!
I took home my 2015 Leaf SV mid-December here in Maryland. Drove it 300 miles without issue, if I recall correctly. Then I went out of town for the holidays. Came back and I occasionally experience loss of acceleration like you guys are saying, except mine has always been restored within seconds of it occurring. It only happens after sitting at a stop sign or stop light for more than 30 seconds. It actually happens in two distinct failure modes:
(1) Move my foot from brake to throttle, and there is no power at all for between 1/4 and 2 seconds, then it is restored. This symptom seems to happen more often when it is below 25 degrees out, and it has been sitting cold for a while. No alarms or lights come on.
(2) Move my foot from brake to throttle, and there is a burst of power, then it drops out and limps along at about 3kw motor power (and also limits regen to this amount, if I lift my foot). After 3-12 seconds, full power returns, but I think the duration is getting longer. I used to think tapping the brake pedal and going back to the throttle reset it, but I'm not sure that helps anymore. Now it stays in "evil turtle" mode across the whole intersection, and I have to put on my flashers so people don't rear-end me. This symptom normally happens after it has been driven for about 20 minutes already, and has happened even at 40 degrees (the hottest it's been here all winter). No alarms or lights come on, but you can see the limited power output on the energy gauge.
I took it to my dealer on January 29 (the #1 Leaf dealer on the East Coast, so they of all people should know what they're doing). They did not see any error codes in the computer, but agreed this sounded like a serious problem. They kept it for a five days, but were not able to duplicate the problem in the ~10 minute test drives they took every morning (trying to get the first symptom after a long cold soak). I came and did a test drive with the service manager (but without the tech in the car) and he saw it happen, so he agreed to keep the car. Two days later, they still had not replicated it with the tech in the car, and told me they couldn't replace any parts under warranty without the data and to come back when it got worse.
They apparently had run it by the Nissan service rep, who had the same hunch--that it was related to the rear brake sensor (???) which would disable the throttle if moisture was trapped in it. This might explain the first symptom but not really the second.
Since then, it has happened 9 times, and happens 3 or 4 times during the course of an entire 80-mile discharge.
I just ordered a Freematics OBD-II Logger in the hopes of capturing all the Car-CAN messages, to see if anything shows up about the throttle position sensor or brake sensors or whatever. Here's hoping something useful shows up. At this rate, though, I should be able to take it to them in a week or two with instructions to drive it for a whole battery and they'll be guaranteed to see it.