I have a method that processes a list of entities and checks if they are valid or not. Invalid entities are added to a HashSet. Later, I attempt to filter out these invalid entities from the original list, but the filtering doesn’t work correctly — invalid entities are still present in the final list.

I found an issue, fixed it, but I got warnings afterwards.

PersonSyncService.cs

 protected override async Task Add(List<(PersonEntity dest, PersonSyncModel src)> entities)
 {
     var invalidEntities = new HashSet<(PersonEntity dest, PersonSyncModel src)>();
     //Irrelevant code is removed from this post

     //This is where the problem is. entitesToAdd needs to be 0 because invalidEntities and entities consist of same elements. 
     //For example, if the count of entities is 5, invalidEntities is also 5. 
     //entitiesToAdd should have no elements. But in this code, it would be 5. 
     var entitiesToAdd = entities.Where(entity => !invalidEntities.Contains(entity)).Select(e => e.dest).ToList();
     await Repository.InsertAsync(entitiesToAdd);

     //Rest of the code
 }

Problem is, that PersonEntity inherits from EntityBase class. In which there is a custom implementation of Equals and GetHashCode. This is current version :

public abstract class EntityBase<TKey> : IEntity<TKey>, IEquatable<IEntity<TKey>>
{
    public virtual TKey Id { get; set; }

    // Custom equality comparison for IEntity<TKey>
    public virtual bool Equals(IEntity<TKey> x, IEntity<TKey> y)
    {
        if (ReferenceEquals(x, y)) return true;
        if (ReferenceEquals(x, null) || ReferenceEquals(y, null)) return false;
        return EqualityComparer<TKey>.Default.Equals(x.Id, y.Id);
    }

    // Custom equality comparison with another IEntity<TKey>
    public virtual bool Equals(IEntity<TKey> other)
    {
        if (ReferenceEquals(this, other)) return true;
        if (ReferenceEquals(other, null)) return false;
        return EqualityComparer<TKey>.Default.Equals(Id, other.Id);
    }

    // Equality comparison with an object
    public override bool Equals(object obj)
    {
        if (ReferenceEquals(this, obj)) return true;
        if (obj == null || obj.GetType() != GetType()) return false;

        return Equals(obj as IEntity<TKey>);
    }

    // Consistent GetHashCode implementation
    public override int GetHashCode()
    {
        return EqualityComparer<TKey>.Default.GetHashCode(Id);
    }

    // Implement IEqualityComparer's GetHashCode method
    public int GetHashCode([DisallowNull] IEntity<TKey> obj)
    {
        return EqualityComparer<TKey>.Default.GetHashCode(obj.Id);
    }
}

I have FIXED this issue but the fixed version of my code causes warnings.
Fixed EntityBase :

public abstract class EntityBase<TKey> : IEntity<TKey>, IEquatable<IEntity<TKey>>
{
    public virtual TKey Id { get; set; }

    public virtual bool Equals(IEntity<TKey> x, IEntity<TKey> y)
    {
        // Check whether the compared objects reference the same data
        if (ReferenceEquals(x, y)) return true;

        // Check whether any of the compared objects is null
        if (ReferenceEquals(x, null) || ReferenceEquals(y, null)) return false;

        // Check whether the objects' properties are equal.
        return x.Id.Equals(y.Id);
    }

    public virtual bool Equals(IEntity<TKey> other)
    {
        if (ReferenceEquals(this, other)) return true;
        if (ReferenceEquals(other, null)) return false;
        return this.Id.Equals(other.Id);
    }

    public override bool Equals(Object obj)
    {
        if (obj == null) return false;
        if (obj is not IEntity<TKey> entityObj) return false;
        else return Equals(entityObj);
    }

    protected bool Equals(EntityBase<TKey> other)
    {
        return EqualityComparer<TKey>.Default.Equals(Id, other.Id);
    }

    public int GetHashCode([DisallowNull] IEntity<TKey> obj)
    {
        // Calculate the hash code for the object.
        return obj.Id.GetHashCode();
    }
}

But, now I am getting these warnings :