I used the new mouse actuator and had it used for mouselook. It seems that you would need to turn an amount until the mouselook actually works. My threshold is set to 0, and I am very confused of why this still happens. I would like to have my mouselook start to move as soon as I move my mouse. How can I achieve this?
The issue was related to the way that blender get Screen resolutions (returning integers). Due to this, a little threshold had to be setted internally. Currently, a fix was summitted https://developer.blender.org/rBee58d449455df9470c4a0a902056b8c2001128bf rounding to upper pixel and removing that little intern threshold.
Could you download a dayly build https://builder.blender.org/download/ and check that the issue has been fixed for you?
Note: For a better behaviour, to use a mouse sensor instead of a always sensor
Note2: it's known that with a setup with 2 monitors the mouse look doesn't work correctly. I'm investigating how to fix it.
I also had this problem, and it can be fixed by simply lowering the sensitivity. Note that the reset distance is still smaller than the trigger distance, so this does not fix the problem completely, it only makes almost un-noticable and more bearable.
With problem Improved
The reason this happens is that the game engine, when calculating the mouse's movement, resets the mouse to the center of the screen slightly before it detects the new position. If you do not move the mouse fast enough, the game engine resets the cursor to the center before it can detect it's movement.