I have just got my Aventon Level delivered and had the same problem.
Besides the display flashing in 1 sec, it was also inconsistent. Did not turn on sometimes at all. First I thought that the battery was dead/empty or malfunctioning. But when I plugged in the adapter, the light was always green. After leaving the battery on charge overnight (thinking that maybe the battery balance is not there, thus the green light) and experiencing the same thing, with no replies from Aventon I was about to lose it.
Then I read
@Amptech's post here and decided to try it. I made a tiny hinge from a paperclip, wrapped the handle with tape, and pulled the metal contacts in the battery to bend them to a slight angle so that they could touch the male connectors on the bike.
And it worked! The battery was indeed fully charged. And I also noticed that the battery sat firmer than before ~ I can't say that I love the battery actually being supported by these thin metal connectors. This might happen again. So my theory here is that the bike should have had too much horizontal force and the connectors in the battery were bent to the walls by the male connectors that are on the bike.
Sharing because I felt your pain. Think twice before trying
Cheers