Unexpected ScriptableObject Behaviour

I am currently working on a game which should be your basic RPG style and in this game I am using an Ability system based on ScriptableObjects. Each Ability has its own ParticleSystem (prefab) and AudioSource.

Basically all Ability.asset files are added to a list of Abilities. Using PageUp/Down buttons the player equips the next/previous Ability of the List.

When "Fire1" is pressed the ability is then cast which works just fine before equipping the next Ability. Then, no matter how many times I press "Fire1" no Ability is cast unless I click out of game-view and inside of it again. However in the Inspector everything seems OK.

Here's my code:

void Update ()
{
    abilityCount = AbilitySystem.Instance.allAbilities.Count - 1;
    abilityCooldown -= Time.deltaTime;
    if(Input.GetButtonDown("Fire1") && abilityCooldown <= 0f)
    {
        Shoot();
        abilityCooldown = 1f / castingSpeed;
    }

    if (Input.GetKeyDown(KeyCode.PageDown))
    {
        abilityIndex--;
        if (abilityIndex < 0)
        {
            abilityIndex = abilityCount;
        }
        currentAbility = AbilitySystem.Instance.allAbilities[abilityIndex];
        UpdateAbilityStats();
    }

    if (Input.GetKeyDown(KeyCode.PageUp))
    {
        abilityIndex++;
        if (abilityIndex > abilityCount)
        {
            abilityIndex = 0;
        }
        currentAbility = AbilitySystem.Instance.allAbilities[abilityIndex];
        UpdateAbilityStats();
    }

}

void UpdateAbilityStats()
{
    abilityDamage = currentAbility.abilityDamage;
    abilityRange = currentAbility.abilityRange;
    abilityCooldown = currentAbility.abilityCooldown;
    particles = currentAbility.Particles;
    particlesOnTarget = currentAbility.onTargetParticles;
}