Well, poop! I'm sorry you are having issues with your new scale! I have no idea why yours would power down after 3 seconds of no use. Mine does not do that in the least. In fact, I have been waiting for mine to power off during mixing and it never has. I feel bad that you may have gotten a bad unit.
But hey, if it makes you feel any better, my new vapor flask mod (used for 5 days) just took a dump on me. It just went belly up, right in the middle of my vaping enjoyment. $70/5 = $14 dollars a day.....then the the sound of a toilet flushing rushed through my ears! I feel your pain!