To recreate:
run the game
press up (or w) to move the paddle upwards, and hold it until the paddle gets stuck in a wall.
When the paddle moves into the top wall, it keeps slowly moving upwards, until it disappears of the screen. When the paddle moves into the bottom wall, it keeps moving slowly upwards until it comes back into the playing area. These are probably caused by the same bug, but check and make a new issue if they're not.
To recreate: run the game press up (or w) to move the paddle upwards, and hold it until the paddle gets stuck in a wall.
When the paddle moves into the top wall, it keeps slowly moving upwards, until it disappears of the screen. When the paddle moves into the bottom wall, it keeps moving slowly upwards until it comes back into the playing area. These are probably caused by the same bug, but check and make a new issue if they're not.