Hi!
When I start the game in window mode with the cursor visible the window doesn’t lock the mouse to the window’s viewport. If I toggle to fullscreen and back to window mode again, the mouse is now locked to the window. I don’t know if this is the desired behavior but I would guess it’s not.
This has been marked as closed as a duplicate!
Thanks!
It would be nice to have a link to the duplicate question 
Since this post is pretty out-dated and was never closed out officially, if you are still experiencing a similar issue in a more recent version of the engine, please create a new answerhub post and provide me with a link in your response.
This way it can be tracked more effectively and I can assist you with troubleshooting. Let me know if you have further questions or need additional assistance.
Cheers,