See test Entity_equality_through_subquery_composite_key:

ctx.Orders
    .Where(o => o.OrderDetails.FirstOrDefault() == new OrderDetail
    {
        OrderID = 10248,
        ProductID = 11
    })
    .ToList());

Since OrderDetail has a composite key, the subquery would be evaluated twice.

We should be able to properly translate this by pushing the entity equality's column comparisons into the subquery.