EF Core 2.0 - filtering IQueryable navigation property collection empty

Tech:

• EF Core 2.0.0
• Asp.Net Core Mvc 2.0.0

When i execute this method it throws "InvalidOperationException: Sequence contains no matching element" on evaluating CurrentGrade. Why does it throw and how can I fix it?

I have a search method filtering on quite a lot of properties on a large dataset (10 000 users with thousands of related entities). I'm trying to optimize the query and i don't want to execute the query until all filtering has been made. While using ToList() makes the method work i would rather work against an IQueryable and execute the query when done filtering.

I'm pretty sure this worked before updating EF Core from 1.x to 2.0.

  public MemberQueryResult Search(MemberQuery filter)
        {
            var query = Context.Users
                .Include(x => x.Honours)
                .Include(x => x.Grades)
                .Include(x => x.Strokes)
                .Include(x => x.Posts)
                .Include(x => x.Loge)
                .AsNoTracking();

            query = query.ApplyFiltering(filter);

            return result;
        }

ApplyFiltering() works well for filtering on foreign keys but when filtering on a navigation property collection using .Where() it throws on ICollection Grades on Member when just before the filtering it was included.

This is the method inside ApplyFiltering() that throws:

  private static IQueryable<Member> SearchByCurrentGradeRange(MemberQuery filter, IQueryable<Member> result)
    {
        if (filter.GradeRange == null) return result;

        var gradeRange = filter.GradeRange.Split(',');
        var gradeFrom = (Grade)int.Parse(gradeRange[0]);
        var gradeTo = (Grade)int.Parse(gradeRange[1]);

        result = result.Where(x => x.CurrentGrade >= gradeFrom && x.CurrentGrade <= gradeTo);

        return result;
    }

CurrentGrade is a calculated property on a member, Grade is just an enum.:

    public sealed class Member : IdentityUser
{
        public Grade CurrentGrade => Grades.OrderBy(x => x.Grade).Last(x => x.ReceivedDate != null).Grade;

        public ICollection<MemberGrade> Grades { get; set; } = new Collection<MemberGrade>();

}