So I finally figured out how to disable this obnoxious console spam. It mainly occurs when playing as L4D1 characters as from what I can tell, the scene files weren't configured correctly and thus it spews errors left and right. The simple 'fix' is to just mark the file the game pulls the scene information from as missing, which from what I can tell only has one drawback of disabling facial animations for the L4D1 characters. If you're fine with that, here's what you have to do: Make sure your game is closed to begin with. Navigate to (Steam Directory)\steamapps\common\Left 4 Dead 2\left4dead2_dlc2\scenes and find the file named 'scenes.image'. Simply rename the file to anything else (I called mine 'scenes_b.image'). Then go to (Steam Directory)\steamapps\common\Left 4 Dead 2\left4dead2_dlc3\scenes and do the same thing with the 'scenes_image' file in that folder too. This will prevent the majority of the StartGestureSceneEvent console errors. If you want to be absolute, you can go to (Steam Directory)\steamapps\common\Left 4 Dead 2\left4dead2_dlc1\scenes and do the same thing again, but this will probably start disabling some facial animations for L4D2 characters that are exclusively used in The Passing campaign. To revert the changes, close the game and rename the files back to 'scenes.image'.