Laggy Game Movement

[game_slayer_99]

I've noticed that the movement in my Pong game is experiencing a strange amount of lag when I start the game up in Python, despite coding it to run at 60 fps. I converted the game to an .exe file and found that it's still experiencing this same lag. However, I added code to print the fps on the screen and it's telling me that it is running at 60 fps. What's most strange however is if I open the .exe file a second time so that the game is running twice in two different windows, the gameplay is notably smoother. As soon as I close the second window, the gameplay again returns to its normal laggy self. I think this is more of an issue with the computer rather than Python but I don't know enough to diagnose the issue or how I can fix this. I've tested the game on three other computers and none of them have this issue. If someone could help that would be great.