Which 46" deck? 2 blade or 3? How is the deck pitched? Mulching or bagging? A better description of the cut or pics may help.

Check for a missing deck pin and spring clip on one of the corners? The ones you remove to pull the deck off the frame. That would do it.

Put it on a flat driveway and measure the rim height of the decks all around. Also pull the blades around underneath and check for how close they are to the deck bottom edge. Now then, you gotta check the blades height in the middle of the deck as if maybe a blade didn't seat straight on it's shaft. This is a case of "Look fer it'. What you need to look for is the blade (s) height from the ground being the same all around in the entire cutting circle from the middle hole to the outside.
Wild thought! You don't weight 300 lbs do you? Maybe add some weight to seat before tests to duplicate cutting conditions. LOL