It's a weird bug. I've added a simple fix in the code, but that will already be available in the next update. For now, there are several solutions to this bug. First, set the minigame difficulty to easy in the settings, then try pressing the “Ignore” button on the error screen and then quickly pressing the “Swim” button on the right side of the screen. This should reset the swim progress and fix the minigame. If that doesn't work, the other option is to start a new game over, or else send me your save in a private message in Discord, and I'll manually fix it on your save.