About six months after I got my 2016 Leaf (Extended Range) I noticed that my range had diminished considerably. After unsuccessfull tries to get my dealer's service department to find the problem, I got the LeafSpy Pro app, which promptly showed that one of the cells had failed. I decided to take my leaf to another dealer and the technician found that as shown by LeafSpy, one of the cells had failed and he replaced the cell. All under warranty.
Once again, the car went back to getting the original range, which in my case was around 120 miles per full charge.
Then, a month after I got the car back, another cell short-circuited and the car wouldn't start at all. I towed the Leaf back to the dealer and they once again replaced the bad cell at no cost.
So, if your LeafSpy shows that you have a bad cell, take it in to your service department and have them replace the cell.