Check for DTC error codes with Leaf Spy, if possible. The accelerator pedal sends position information to other modules such as the vehicle control module. If the potentiometers and associated electronics that convert pedal position to digital data are failing, they may work correctly under light to intermediate pedal pressure and fail to signal fully-depressed position. Under those conditions, the car would seem sluggish in ECO mode and almost normal when not in ECO. There have been just a few reports of accelerator position sensor failures on LEAF's. I have had to replace throttle position sensors a couple of time on gasoline-engine vehicles over the past few years.
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