What causes a record dropped and not being mapped?

[wyf5188]

I have a list of 33 dynamic objects retrieved from Dapper and try to use Slapper.AutoMapper.MapDynamic(dval, false).ToList(), but find three records are dropped. So the Slapper.AutoMapper only returns 30 objects. I wonder what causes the 3 records being dropped and un-mapped. I declare the following in TradingDeskDefault class.
[Slapper.AutoMapper.Id]
public long TradingDeskID { get; set; }

The 33 dynamic objects have unique values of TradingDeskID.

Please help. I use: "Slapper.AutoMapper": "1.0.0.9"