As posted here:
http://stackoverflow.com/questions/35863999/query-mongodb-sublists-with-c-sharp-linq-regex

Regex IsMatch does not seem to work on list-properties although the same LINQ query runs fine on a standard list.

I.e. given

public class Car

{ public string Name; public List<string> Colors; }

this only works for plain list LINQ:

var regex = new Regex("^Blue.*");
var matchingCars = carCollection.Where(x => x.Colors.Any(y => regex.IsMatch));

The above just silently returns an empty queryable.