Hi,
yesterday my Surface replacement arrived from Microsoft.
My device was fully replaced and got a new serial number.
I've installed all my tools and apps.
THERE ARE NO ABNORMAL SHUTDOWNS ANYMORE!
The device runs on battery power goes into sleep, when not in use and continous work there, where I left it.
So the resumee is that this behavior is due to an hardware issue and all people who run into this problem, too should immediately open a repair case via the Microsoft website as long as their warranty is still active!
If you don't know how, here's how to to do.
Go to www.microsoft.com and log in with your Microsoft account. In your account go to "devices". If not done yet register your device with its serianumber. To find on the Surface package or on the back of the device behind the Surface Stand. After the the
device is recognized you could open a Support case from there. You'll get a shippment label from there to print and stick it on a parcel.
The exchange of my device took about 4 week days.
Best regards Patrick