The game was never designed to be ran at 120FPS and the game physics bug out when running at this high a framerate, for most of the game this isn't an issue except for here. So the goal is to lower the framerate for this one area so you can get the sub without it exploding.

If your sub has already exploded and you don't have a previous save, you're gonna have to replay the game and get to here again.

First: Create a save other than your quicksave in front of the button.
Second: Bind your quicksave and quickload keys so you can easily reach both.

Now press the button and just after it drops, quicksave and quickload. This will drop your fps and increase the odds of the sub dropping correctly.
If it fails, load the save you created earlier and try again.
I have found it works every single time if your quicksave is in the right spot during the process.

If your quickload looks like this it will drop correctly every single time: