Why does my XBox account automatically log off?

Since a few days something is wrong with my XBox. While playing a game, my account just logs off without me doing anything. Is that perhaps due to poor Wi-Fi or something? I look forward to your answer.

Below is always displayed why you have been logged out, right? Probably it's up to you on the internet. There's still the possibility that you are logged in somewhere else so on another console.