Leave the battery charging overnight to see if maybe the cells will balance and take a charge. If your batt is not at 54v the next day without the charger hooked up, try to follow up on warranty since it sounds brand new.
I think you are worrying too much and not enjoying your e-grin on your new bike that is working great! It is thought to be best practice to only 90% charge and 90%discharge of usable voltage. You will possible double the life of the battery pack. To monitor the pack more you want a watt meter...
The usual bms low voltage cutoff is 2.7v/cell I think. That would mean your pack would die below 42v. I'm half guessing here.
It's best not to stress your pack in either direction though to extend its life.
3 position switch to set output voltage to 58.8V, 57.4V and 53.2V. This enables charging to approx 100%, 90% and 50% SOC. Regularly charging to 90% SOC will help to extend cycle life. Charging to 50% is recommended for battery storage