It happens because the game tries to load a "burning" animation, but the VR training buddies don't have one so the game constantly keeps trying to load a animation that doesn't exist every single frame and it gets super laggy as a result

Also, the fire doesn't get put out because the game can't even register the animation starting so it won't end (since it assumes that it didn't even start yet)

The only solution is to open up the menu and either restart the stage, quit or close the game.