As someone mentioned on SO (https://stackoverflow.com/questions/47313022/mongodb-c-sharp-driver-serializing-listenum-as-string), the following cases are currently not handled by the EnumRepresentationConvention:

List<EnumType> { get; set; }
List<List<List<EnumType>>> { get; set; }
Dictionary<EnumType, OtherType> { get; set; }
Dictionary<OtherType, EnumType> { get; set; }

The convention currently only works on straight Enums as in

EnumType E { get; set; }

and nullable Enums as in:

EnumType? E { get; set; }

This improvement is about making sure that (even nested) collections of the various kinds are affected by the convention as expected.