Random Shutdown on MacBook Air

Hi,

My MacBook Air (early 2014) shut down randomly. That happen after few hours or minute or seconds...

I did every basic things I could do to figure it out, but still. So, I bring it to Apple store. They try every things, but did'n find anything, so they decide to reset my MacBook as a new one.

But even as new MacBook (clean OS, no data, no device...) it still shut down randomly.

After every crash, I can read in my log:

"kernel Previous Shutdown Cause: -6"

Can you help me?