Why C# Expressions Lambda cause memory leak?

Question

I have created the following extension method:

   public static IQueryable<StudioClass> FilterByIdentifiers(this IQueryable<StudioClass> classes, Tuple<Guid,DateTime?>[] identifiers)
        {
            if (identifiers != null)
            {
                var parameter = Expression.Parameter(typeof(StudioClass), "sc");
                var idMemberAccess = Expression.Property(parameter, "Id");
                var dateMemberAccess = Expression.Property(parameter, "DateCreatedUTC");

                //False empty expression
                var expr = Expression.Equal(Expression.Constant(2), Expression.Constant(1));

                foreach (var (identifier, timestamp) in identifiers)
                {
                    if (timestamp.HasValue)
                    {
                        var complexExpression = Expression.AndAlso(Expression.Equal(idMemberAccess, Expression.Constant(identifier)),
                            Expression.Equal(dateMemberAccess, Expression.Constant(timestamp.Value)));
                        expr = Expression.OrElse(expr, complexExpression);
                    }
                    else
                    {
                        expr = Expression.OrElse(expr, Expression.Equal(idMemberAccess, Expression.Constant(identifier)));
                    }
                }

                var lambda = (Expression<Func<StudioClass, bool>>)Expression.Lambda(expr, parameter);
                classes = classes.Where(lambda);
            }

            return classes;
        }

We have identified that this creates a memory leak, and I can't understand why. Hope somebody can help me identify the problem or point me to some resource of why this might be happening.