iPhone X updates itself over night

Hello,

i'm experiencing a very strange bug, my iPhone X (64GB) sometimes seems to update itself over night. If i wake up and check my phone i got this white 'Hello/Hola etc. welcome to iPhone screen' and have to agree to the terms and conditions of Apple. Then I can continue to use the Phone normally.

This ONLY happens at night, (I charge my phone in the night), I'm on iOS 11.2 and it's already my second X as i exchanged my first one (256GB) since the bug was so bad that it appeared every night (even after completely resetting the Phone two times). Background App refresh etc. is turned off.

Now my new X is starting to have the same issue after running perfectly for the first 5 days.

Has anybody had this issue before? I already contacted the Apple Support and they seem to be as clueless as me. I really don't know what to do anymore since i already exchanged the Phone and it still seems to be an issue. Maybe my backup is faulty?

Thanx & Greetings