class Class1
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
    public int MId { get; set; }
    public Char Status { get; set; }
}
        IQueryable<Class1> src = null;
        var grp1 = src
            .GroupBy(e => new { Date = e.Date, MId = e.MId })
            .Select(g => new { Date = g.Key.Date, MId = g.Key.MId, Count = g.Count() })
            .Where(e => e.Count > 1);
        //var qu
        IQueryable<Class1> qu
            = src.GroupJoin(grp1,
                ok => new { Date = ok.Date, MId = ok.MId },
                ik => new { Date = ik.Date, MId = ik.MId },
                (ok, ik) => new { Ok = ok, Ik = ik })
            .SelectMany(j => j.Ik.DefaultIfEmpty(), (j, ik) => new { J = j, Ik = ik })
            .Where(e => e.Ik == null || (e.Ik != null && e.J.Ok.Status == 'M'))
            .Select(e => e.J.Ok)
            ;