GetKeyDown Bug

My bug is that the GetKeyDown doesn't work as intended, it seems random when its working or not and I have no idea what could be causing the problem. Code:

 function Update() {
     if (Network.isServer || Network.isClient) {
         ShowInGameGUI = true;
     } else {
             ShowInGameGUI = false
     }
     if (ShowInventory) {
         if (Input.GetKeyDown(KeyCode.Escape)) {
             ShowInventory = false;
             return;
         }
     }
     if (!ShowInventory) {
             if (Holding) {
                 var Holding = false;
                 var CurrentHolding = new item();
                 var CurrentHNumber = -1;
             }
     }
 if (ShowInGameGUI) {
             if ( player == null) {
             player = GameObject.Find(PlayerPrefs.GetString("Username"));
             }
     //Show in-game GUI
     if (Input.GetButtonDown("Inventory")) {
         if (ShowPauseMenu) {
             return;
         }
         ShowInventory = !ShowInventory;
     }
     if (Input.GetButtonDown("Cancel")) {
         if (ShowInventory) {
             ShowInventory = false;
             return;
         }
         ShowPauseMenu = !ShowPauseMenu;
     }
     if (ShowPauseMenu || ShowInventory) {
         mouse(false);
         //It seems like these lines are making the game unfocus, so each time you toggle the inventory you will need to click on the game again.
         Screen.lockCursor = false;
         Screen.showCursor = true;
     } else {
         mouse(true);
         Screen.lockCursor = true;
         Screen.showCursor = false;
     }
 }
 }

Would the GUI Code help finding the issue?, maybe some overload when calling or something...