Steps:

• Create an entity with a subdocument
• Query on a field in that entity
• Exception with serialization error thrown
• Note: Querying on fields in parent document works as expected

Minimal Repro:

https://github.com/RainCityHousing/QueryOnSubdocumentMember

Call Stack:

Unhandled exception. System.InvalidOperationException: Serializer for NestedDocumentTest does not have a member named NestedItem.
   at MongoDB.Driver.Linq.Linq3Implementation.Misc.DocumentSerializerHelper.GetMemberSerializationInfo(IBsonSerializer serializer, String memberName)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MemberExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, MemberExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MemberExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, MemberExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.BinaryExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, BinaryExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.ExpressionToAggregationExpressionTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateUsingAggregationOperators(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.Translate(TranslationContext context, Expression expression, Boolean exprOk)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.ExpressionToFilterTranslator.TranslateLambda(TranslationContext context, LambdaExpression lambdaExpression, IBsonSerializer parameterSerializer, Boolean asRoot)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.WhereMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.SelectMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.AsMethodToPipelineTranslator.Translate(TranslationContext context, MethodCallExpression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToPipelineTranslators.ExpressionToPipelineTranslator.Translate(TranslationContext context, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToExecutableQueryTranslators.ExpressionToExecutableQueryTranslator.Translate[TDocument,TOutput](MongoQueryProvider`1 provider, Expression expression)
   at MongoDB.Driver.Linq.Linq3Implementation.MongoQuery`2.Execute()
   at MongoDB.Driver.Linq.Linq3Implementation.MongoQuery`2.GetEnumerator()
   at MongoDB.EntityFrameworkCore.Query.QueryingEnumerable`2.Enumerator.MoveNextHelper()
   at MongoDB.EntityFrameworkCore.Query.QueryingEnumerable`2.Enumerator.MoveNext()
   at MongoDB.Bson.Serialization.Serializers.EnumerableSerializerBase`2.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TValue value)
   at MongoDB.Bson.Serialization.Serializers.DiscriminatedWrapperSerializer`1.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TValue value)
   at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Serialize[TValue](IBsonSerializer`1 serializer, BsonSerializationContext context, TValue value)
   at MongoDB.Bson.Serialization.Serializers.EnumerableSerializerBase`2.Serialize(BsonSerializationContext context, BsonSerializationArgs args, TValue value)
   at MongoDB.Bson.Serialization.Serializers.SerializerBase`1.MongoDB.Bson.Serialization.IBsonSerializer.Serialize(BsonSerializationContext context, BsonSerializationArgs args, Object value)
   at MongoDB.Bson.BsonExtensionMethods.ToJson(Object obj, Type nominalType, JsonWriterSettings writerSettings, IBsonSerializer serializer, Action`1 configurator, BsonSerializationArgs args)
   at MongoDB.Bson.BsonExtensionMethods.ToJson[TNominalType](TNominalType obj, JsonWriterSettings writerSettings, IBsonSerializer`1 serializer, Action`1 configurator, BsonSerializationArgs args)
   at Program.<Main>$(String[] args) in C:\Users\sbrophy\source\repos\QueryOnSubdocumentMember\QueryOnSubdocumentMember\Program.cs:line 28