I cannot reproduce it consistently but every now and then I start the game, press play in the launcher, load my singleplayer world and it does load at first. But as soon as the loading screen is done and I'm in my world, it is super laggy and takes really long for me to even move my cursor a little bit. So I just let it load. But sometimes I come back to my PC and nothing moves anymore, as though my mouse was turned off, but I also checked a different mouse and I still had this issue once. When I tab out of the game I can't tab back in, I just get a grey screen.