Collision issues following Unity's platformer controls tutorials

I've been building a pretty simple platformer, and followed these tutorials for my player controls - https://learn.unity.com/tutorial/live-session-2d-platformer-character-controller

I've noticed a bug that I can't pin down because it happens so rarely I can't figure out the cause. It also happens so rarely, I haven't managed to capture a recording of it, so I'll try to describe it.

Sometimes it happens when the player is standing near a wall, and jumps up against it. The player then passes diagonally up and through the wall very slowly until they're standing on top of the block.

Sometimes it happens when they're jumping alongside a wall. So, if they're stood with the end of a platform above them, and to one side, they should be able to jump up past it, as they don't actually hit it. But sometimes, they sort of hit it, and stop going up, but also don't fall down. So they just sort of hover for the length of a full jump before falling back down.

It was a long time ago in the development that I followed the tutorial, so I can't remember every minor change, but I think all I changed was to add in my pause system.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class PhysicsObject : MonoBehaviour {
6.  
7.     //gravity
8.     public float gravityModifier = 1f;
9.     protected bool grounded;
10.     protected Vector2 groundNormal;
11.     public float minGroundNormalY = 0.65f;
12.  
13.     //movement
14.     protected Rigidbody2D myRigidbody;
15.     protected Vector2 targetVelocity;
16.     protected Vector2 velocity;
17.     protected const float minMoveDistance = 0.001f;
18.     protected float moveVelocity = 0f;
19.  
20.     //speed up slow down
21.     protected float SpeedUp = 0.1f;
22.     protected float groundSlowDown = 0.05f;
23.     protected float airSlowDown = 0.2f;
24.  
25.     //collisions
26.     protected ContactFilter2D contactFilter;
27.     protected RaycastHit2D[] hitBuffer = new RaycastHit2D[16];
28.     protected List<RaycastHit2D> hitBufferList = new List<RaycastHit2D> (16);
29.     protected const float shellRadius = 0.01f;
30.  
31.     //pause system
32.     protected PauseSystem pauseSystem;
33.  
34.     void OnEnable ()
35.     {
36.         //get rigidbody
37.         myRigidbody = GetComponent<Rigidbody2D> ();
38.     }
39.  
40.     protected void Start ()
41.     {
42.         //set up contact filter
43.         contactFilter.useTriggers = false;
44.         contactFilter.SetLayerMask (Physics2D.GetLayerCollisionMask (gameObject.layer));
45.         contactFilter.useLayerMask = true;
46.  
47.         //get pause system
48.         pauseSystem = FindObjectOfType<PauseSystem> ();
49.     }
50.  
51.     protected void Update ()
52.     {
53.         targetVelocity = Vector2.zero;
54.         ComputeVelocity ();
55.     }
56.  
57.     protected virtual void ComputeVelocity ()
58.     {
59.        
60.     }
61.  
62.     protected void FixedUpdate ()
63.     {
64.         if (!pauseSystem.isPaused || pauseSystem.gameEnd)
65.         {
66.             //movement
67.             velocity += gravityModifier * Physics2D.gravity * Time.deltaTime;
68.             if (targetVelocity.x != 0)
69.                 velocity.x = Mathf.SmoothDamp (velocity.x, targetVelocity.x, ref moveVelocity, SpeedUp);
70.             else
71.                 velocity.x = Mathf.SmoothDamp (velocity.x, targetVelocity.x, ref moveVelocity, grounded ? groundSlowDown : airSlowDown);
72.  
73.             grounded = false;
74.  
75.             Vector2 deltaPosition = velocity * Time.deltaTime;
76.             Vector2 moveAlongGround = new Vector2 (groundNormal.y, -groundNormal.x);
77.  
78.             //horizontal
79.             Vector2 move = moveAlongGround * deltaPosition.x;
80.             Movement (move, false);
81.  
82.             //vertical
83.             move = Vector2.up * deltaPosition.y;
84.             Movement (move, true);
85.         }
86.     }
87.  
88.     void Movement (Vector2 move, bool yMovement)
89.     {
90.         //get movement distance
91.         float distance = move.magnitude;
92.  
93.         //collision check
94.         if (distance > minMoveDistance)
95.         {
96.             int count = myRigidbody.Cast (move, contactFilter, hitBuffer, distance + shellRadius);
97.  
98.             hitBufferList.Clear ();
99.             for (int i = 0; i < count; i++)
100.                 hitBufferList.Add (hitBuffer [i]);
101.  
102.             for (int i = 0; i < hitBufferList.Count; i++)
103.             {
104.                 Vector2 currentNormal = hitBufferList [i].normal;
105.  
106.                 //grounded
107.                 if (currentNormal.y > minGroundNormalY)
108.                 {
109.                     grounded = true;
110.                     if (yMovement)
111.                     {
112.                         groundNormal = currentNormal;
113.                         currentNormal.x = 0f;
114.                     }
115.                 }
116.  
117.                 //collision
118.                 float projection = Vector2.Dot (velocity, currentNormal);
119.                 if (projection < 0f)
120.                 {
121.                     velocity = velocity - projection * currentNormal;
122.                 }
123.  
124.                 float modifiedDistance = hitBufferList [i].distance - shellRadius;
125.                 distance = modifiedDistance < distance ? modifiedDistance : distance;
126.             }
127.         }
128.  
129.         //move rigidbody
130.         myRigidbody.position = myRigidbody.position + move.normalized * distance;
131.     }
132. }
133.