When I try to build a new project, the camera just rotates in the build, but the camera does not do the same thing when I play the level. There is no commands coming from my mouse nor my keyboard, but it just keeps rotating.
We see this issue pop up quite often, and in most cases it is caused by a gamepad or joystick. If you have one, try unplugging it and open the editor again.
If that fixes it, you might want to re-calibrate the joystick/gamepad in Windows, the sticks have a “dead zone” where input is ignored because some sticks are not perfectly straight, or can move slightly without any force. As they get older this dead zone expands, and UE4 thinks it is actual input. In game uses a different setup from the editor itself, so that is why it can happen in one but not the other. Go to Edit - Project Settings - Input and click the small down arrow to expand the main category, from here you can adjust the dead zone amounts (but this only applies for “in game”, calibrate in Windows should help for the editor).
Let us know if that helps!