CalculateFinalValue_Updated.cs

private float CalculateFinalValue()
{
    float finalValue = BaseValue;
    float sumPercentAdd = 0; // This will hold the sum of our "PercentAdd" modifiers

    for (int i = 0; i < statModifiers.Count; i++)
    {
        StatModifier mod = statModifiers[i];

        if (mod.Type == StatModType.Flat)
        {
            finalValue += mod.Value;
        }
        else if (mod.Type == StatModType.PercentAdd) // When we encounter a "PercentAdd" modifier
        {
            sumPercentAdd += mod.Value; // Start adding together all modifiers of this type

            // If we're at the end of the list OR the next modifer isn't of this type
            if (i + 1 >= statModifiers.Count || statModifiers[i + 1].Type != StatModType.PercentAdd)
            {
                finalValue *= 1 + sumPercentAdd; // Multiply the sum with the "finalValue", like we do for "PercentMult" modifiers
                sumPercentAdd = 0; // Reset the sum back to 0
            }
        }
        else if (mod.Type == StatModType.PercentMult) // Percent renamed to PercentMult
        {
            finalValue *= 1 + mod.Value;
        }
    }

    return (float)Math.Round(finalValue, 4);
}