I'm trying to make a 2D fight game, and it only recognize 2 inputs at the same time

Hello there. As the title said, for some reason the script I've created only recognize the first 2 of the 3 inputs I make at the same time. I'm not very good at programing, that means I have no idea if the problem comes from unity or from the script so, I'll attach it here:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class InputFixer : MonoBehaviour {
     [SerializeField]
     public List <ControllerInput> PlayerButtons = new List<ControllerInput> ();
     [SerializeField]
     public List <ControllerInput> PlayerDirectionButtons = new List<ControllerInput> ();
     [SerializeField]
     public List <ListInput> InputList = new List<ListInput> ();
     public float inputTime;
     // Use this for initialization
     void Start () {
         
     }
 
     void FixedUpdate (){
         foreach (ControllerInput input in PlayerButtons) {
             if (Input.GetKeyDown (input.button)) {
                 if (InputList.Count != 0) {
                     InputList.Add (new ListInput (input.input, inputTime));
                 } else {
                     InputList.Add (new ListInput (input.input, inputTime));
                 }
             }
         }
         if (Input.GetKeyDown (PlayerDirectionButtons [0].button) || Input.GetKeyDown (PlayerDirectionButtons [1].button) || Input.GetKeyDown (PlayerDirectionButtons [2].button) || Input.GetKeyDown (PlayerDirectionButtons [3].button) ||
             Input.GetKeyUp (PlayerDirectionButtons [0].button) || Input.GetKeyUp (PlayerDirectionButtons [1].button) || Input.GetKeyUp (PlayerDirectionButtons [2].button) || Input.GetKeyUp (PlayerDirectionButtons [3].button)) { 
             #region DPad
             if (Input.GetKey (PlayerDirectionButtons [0].button) && !Input.GetKey (PlayerDirectionButtons [3].button) && !Input.GetKey (PlayerDirectionButtons [1].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.Up) {
                         InputList.Add (new ListInput (InputNames.Up, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.Up, inputTime));
                 }
             } else if (Input.GetKey (PlayerDirectionButtons [1].button) && !Input.GetKey (PlayerDirectionButtons [0].button) && !Input.GetKey (PlayerDirectionButtons [2].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.Right) {
                         InputList.Add (new ListInput (InputNames.Right, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.Right, inputTime));
                 }
             } else if (Input.GetKey (PlayerDirectionButtons [2].button) && !Input.GetKey (PlayerDirectionButtons [1].button) && !Input.GetKey (PlayerDirectionButtons [3].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.Down) {
                         InputList.Add (new ListInput (InputNames.Down, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.Down, inputTime));
                 }
             } else if (Input.GetKey (PlayerDirectionButtons [3].button) && !Input.GetKey (PlayerDirectionButtons [2].button) && !Input.GetKey (PlayerDirectionButtons [0].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.Left) {
                         InputList.Add (new ListInput (InputNames.Left, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.Left, inputTime));
                 }
             } else if (Input.GetKey (PlayerDirectionButtons [1].button) && Input.GetKey (PlayerDirectionButtons [2].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.DwnRgt) {
                         InputList.Add (new ListInput (InputNames.DwnRgt, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.DwnRgt, inputTime));
                 }
             } else if (Input.GetKey (PlayerDirectionButtons [2].button) && Input.GetKey (PlayerDirectionButtons [3].button)) {
                 if (InputList.Count != 0) {
                     //if (InputList [InputList.Count - 1].name != InputNames.DwnLft) {
                         InputList.Add (new ListInput (InputNames.DwnLft, inputTime));
                     //}
                 } else {
                     InputList.Add (new ListInput (InputNames.DwnLft, inputTime));
                 }
             }
             #endregion
         }
     }
     // Update is called once per frame
     void Update () {
         for (int i = 0; i < InputList.Count; i++) {
             InputList [i].timeToGo -= Time.deltaTime;
             if (InputList [i].timeToGo <= 0) {
                 InputList.RemoveAt (i);
                 i--;
             }
         }
     }
 }
 [System.Serializable]
 public class ListInput {
     public InputNames name;
     public float timeToGo;
 
     public ListInput (InputNames _name, float _time){
         name = _name;
         timeToGo = _time;
     }
 }
 [System.Serializable]
 public class ControllerInput {
     public string name;
     public InputNames input;
     public KeyCode button;
 
     public ControllerInput (string _name, InputNames _input, KeyCode _active){
         name = _name;
         input = _input;
         button = _active;
     }
 }
 public enum InputNames{
     Up,
     Down,
     Left,
     Right,
     DwnRgt,
     DwnLft,
     X,
     Triangle,
     Circle,
     Square,
     R1,
     R2,
     R3,
     L1,
     L2,
     L3,
     Start,
     Select,
 }

Thank you.