Youxin Little Magic Sq1s use a Nylon nut(which is borderline criminal for a premium Sq1 because we know that's a bad idea for at least 9 years now), or at least the two I own do. The threads on these strip out after some time, which would explain why it exploded and continues to do so.
Of course, without pictures, that can only be a guess. Maybe the nut just unsrewed and you lost it?
If one of these happened, your best guess would be to buy a proper locknut. I'll check tomorrow, but cube manufacturers somehow are keen on using imperial screws(which is completely idiotical but I won't get into why) and I don't know if the Planet mars stocks metric or imperial nuts in their hardware stores.