Most issues with the shifting system can be fixed by simply calibrating the system. The whole process takes about a minute and your bike's shifting system will adjust itself.
During this process, the wheel needs to be turning the whole time; I usually just tip the bike up on its kickstand so the rear wheel is off the ground and hold the throttle. You can also do this while riding the bicycle on flat, smooth ground in pedal-assist 0 or 1.
Calibrating the Automatic N380 Shifting System:
1. Turn system power on (display powered on).
2. Pedal the bicycle lightly through the entire calibration procedure - have the rear wheel off the ground while pedaling, you can lean the bike over on the kickstand with the help of a friend.
3. Press and hold the "mode" button (the silver/chrome button on the shifter) until the display on the shifter shows hash marks moving from side to side (7 seconds typically), then release the button.
4. Continue pedaling (or start to pedal) lightly while the system shifts from "low" to "high" ratio multiple times and completes the calibration.
You should hear the hub interface (black part by the wheel) make some noise during this process. Once complete, the shifter will stop flashing. If unsuccessful, unplug the interface down by the wheel, and reconnect - then repeat the procedure.
Here's a video on the procedure:
Here is a link to download the complete manual for your reference: