Overview
By default the game doesn’t allow the sticks of an xbox gamepad to function properly. By loading the default gamepad support profile, your pad will work as normal.
How to fix Xbox Support
Run the game. Open the steam overlay. Choose controller configuration in the top right. Choose a new profile for the gamepad you use. Select the default gamepad profile (‘for games with controller support’) from the list. Return to the game. Check to see if the sticks are now functioning properly.