This maybe because you've opened the power-saving function to save the power.
So the camera will be turned off automatically if there is no operation in three minutes. You can choose to turn off this option by App or OSD menu.
Method1: turn off Power-saving by App
1. Link the App and click the Setting icon.
2. Go to General > Auto shutdown and click.
3. Choose 'off'.
Method2: turn off Power-saving by OSD menu
1. There is an option power-saving in the OSD menu like this:
2. When you choose it, you will see this interface:
3. And please choose off, this function will be turned Off.