More research is needed, but it appears that System.Reflection.Emit may not actually work on .NET Standard (it will only work on .NET Framework and .NET Core). Craig has suggested that we can remove the code in BsonMemberMap and compile a Linq expression tree instead

It's likely that most of our customers are either using .NET Framework and .NET Core, so this is not a high priority bug.

More information can be found here:
https://github.com/dotnet/corefx/issues/29365