This ebikes are quite rare in the Us. I do like them and had tested this model.
Try checking the battery contacts on the frame and in the battery; sometimes they get misalignet or a bit outward and therefore it results in a lost connection and no display. But you do get 1sec of display, could be that a cell in the baytery pack is bad.
May need to open the oack and disco/reconect the BMS. But that will void the warranty if it has a void sticker on the battery pack.