Hello, I'm going to post this in case it helps anyone. If you get slowdown or lag in WWP (it happens on the Custom levels like "Beach" as soon as you shoot a bazooka and it explodes) to the tune of 3fps, here is how to fix it: you have connected a controller that the game doesn't like.
As soon as I disconnected my Madcatz controller the lag did not appear. Note that the game doesn't detect controllers being disconnected/reconnected so when you do that you must restart the console.
Hope it helps someone out there googling this in 2 decades' time
