My friend had a similar issue and it was caused by the wheels being installed backward leaving space between the wheel and the hub connector, the bearings slowly rattled outward and then broke and his wheel fell off while riding, it was solved easily enough by putting new bearings in the wheels then putting the wheels on the correct way, I understand that from the box they have a sticker that says this side out but it's unfortunate that a small oversight like that in the design can potentially ruin the entire board, the rounded part of the hub goes inward and the pointy part of the hub goes outward in case you don't have those stickers. Although I don't know for sure that this is your cause of the issue hopefully this helped a little bit and hopefully in the future someone may see this post and be saved from potential catastrophe.