That's funny - I ran into the same "fuzziness" problem initially myself, but thought I'd fixed it by making the dice bigger. The first setup I had was about half the size (and also made for too many bricks on screen). Is your monitor 1920x1080? That's what I'm using (albeit at 75Hz).
Dice are supposed to spawn a short distance from the paddle, sit for a second, then launch towards the paddle (giving the player a rare chance to aim a shot with some degree of precision). I suspect the ones that just stay floating may be getting nudged away from the paddle just before launching, meaning that the force towards the paddle simply cancels out whatever force nudged them in the wrong direction - unfortunately dice that start bouncing horizontally can often do that. I think if I were to put this together again I'd probably not use an actual physics engine to handle the collisions, though it did save a ton of time just for the jam.