CapsuleCollider2D hitbox fails to trigger when player/enemy are stationary

Myself, I wouldn't use a collider toggled on and off for something you want to detect collisions only on certain frames. I'd use a physics overlap query.

Here's a way you could make a script that acts a bit like a capsule collider, but instead of checking for collisions when things move, it checks when you call CheckHits(), returning you a count of matching hits, and invoking a custom event handler for each one:

using UnityEngine;
using UnityEngine.Events;


public class HitCapsule2D : MonoBehaviour {

    [Tooltip(@"x = width (twice the radius), 
y = height (end-to-end distance).
Not affected by scale - always measured in worldspace units.")]
    public Vector2 size = new Vector2(0.5f, 1);

    [Tooltip("Use this to limit the search to only the layers you want to hit.")]
    public LayerMask layersToCheck = (LayerMask)(-1);
    // (Defaults to hitting everything)

    [Tooltip("Handle this event to act on a hit collider.")]
    public UnityEvent<Collider2D> onHit;

    static Collider2D[] _hits = new Collider2D[10];

    // Call this when you want to hit things touching this capsule.
    public int CheckHits()
    {
        // Get the in-plane rotation of the capsule, in degrees.
        var bearing = transform.right;
        float angle = Mathf.Atan2(bearing.y, bearing.x) * Mathf.Rad2Deg;

        // Find all overlapping colliders in the selected layers,
        // using the non-allocating form for efficiency.
        int hitCount = Physics2D.OverlapCapsuleNonAlloc(
            transform.position,
            size,
            CapsuleDirection2D.Vertical,
            angle,
            _hits,
            layersToCheck
        );

        // For each hit found, fire an event to process it.
        for (int i = 0; i < hitCount; i++) {
            onHit.Invoke(_hits[i]);
        }

        // Report back how many hits we got.
        return hitCount;
    }
    
    // Draw a preview of the hit capsule shape.
    void OnDrawGizmos() {
        // Cache the incoming values (this might not be necessary).
        var mat = Gizmos.matrix;
        var col = Gizmos.color;

        Gizmos.color = Color.green;
        // Draw in the capsule's local coordinates - ignoring scale.
        Gizmos.matrix = Matrix4x4.TRS(
            transform.position,
            Quaternion.LookRotation(Vector3.forward, transform.up),
            Vector3.one
        );

        float radius = size.x * 0.5f;
        Vector3 span = new Vector3(0, (size.y - size.x) * 0.5f, 0);

        // Draw the circles at either end of the capsule.
        Gizmos.DrawWireSphere(span, radius);
        Gizmos.DrawWireSphere(-span, radius);

        // Draw the two straight sides of the capsule.
        Vector3 spoke = new Vector3(radius, 0, 0);
        Gizmos.DrawLine(spoke + span, spoke - span);
        Gizmos.DrawLine(-spoke + span, -spoke - span);

        // Put everything back the way we found it.
        Gizmos.matrix = mat;
        Gizmos.color = col;
    }
}