Mongo 3.2 Sub-Document Index issue - mongodb

Question

Recently we have upgraded our MongoDB 2.6(MMAPV1) to 3.2(MMAPV1), After upgrade indexes in sub-document is not working. I did a small proof of concept on both databases with query explain.
In the MongoDB 3.2, the subdocument index is not considered, can anybody suggest the fix for this?
This is sample mongo document,
{
"_id" : ObjectId("58bff13e4e6904293cc206b4"),
"Value" : NumberLong(158),
"OVGuid" : NumberLong(0),
"Name" : "User 08/03/2017 03.55.42.782",
"CreateDate" : ISODate("2017-03-08T11:55:42.783Z"),
"RoleLst" : [
{
"_id" : NumberLong(146),
"Name" : "Role1"
},
{
"_id" : NumberLong(108),
"Name" : "Role2"
},
{
"_id" : NumberLong(29),
"Name" : "Role3"
}
]
}
I inserted nearly 100,000 data with index enabled on "RoleLst._id"(db.User.createIndex({"RoleLst._id":1})) in both Mongo DB 2.6 and 3.2.
Then I tried query explain
db.User.find({ "RoleLst" : { "$elemMatch" : { "_id" :NumberLong(200)}}}).explain()
This is the result I got from 3.2 is
Explain for sub-document query
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "SubDocmentIndexChecking.User",
"indexFilterSet" : false,
"parsedQuery" : {
"RoleLst" : {
"$elemMatch" : {
"_id" : {
"$eq" : NumberLong(200)
}
}
}
},
"winningPlan" : {
"stage" : "COLLSCAN",
"filter" : {
"RoleLst" : {
"$elemMatch" : {
"_id" : {
"$eq" : NumberLong(200)
}
}
}
},
"direction" : "forward"
},
"rejectedPlans" : []
},
"serverInfo" : {
"host" : "******",
"port" : ******,
"version" : "3.2.10",
"gitVersion" : "79d9b3ab5ce20f51c272b4411202710a082d0317"
},
"ok" : 1.0
}
This is the result I got from 2.6
Explain for sub-document query
{
"cursor" : "BtreeCursor RoleLst._id_1",
"isMultiKey" : true,
"n" : 0,
"nscannedObjects" : 0,
"nscanned" : 0,
"nscannedObjectsAllPlans" : 0,
"nscannedAllPlans" : 0,
"scanAndOrder" : false,
"indexOnly" : false,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 0,
"indexBounds" : {
"RoleLst._id" : [
[
NumberLong(200),
NumberLong(200)
]
]
},
"server" : "***********",
"filterSet" : false,
"stats" : {
"type" : "KEEP_MUTATIONS",
"works" : 2,
"yields" : 0,
"unyields" : 0,
"invalidates" : 0,
"advanced" : 0,
"needTime" : 1,
"needFetch" : 0,
"isEOF" : 1,
"children" : [
{
"type" : "FETCH",
"works" : 2,
"yields" : 0,
"unyields" : 0,
"invalidates" : 0,
"advanced" : 0,
"needTime" : 1,
"needFetch" : 0,
"isEOF" : 1,
"alreadyHasObj" : 0,
"forcedFetches" : 0,
"matchTested" : 0,
"children" : [
{
"type" : "IXSCAN",
"works" : 1,
"yields" : 0,
"unyields" : 0,
"invalidates" : 0,
"advanced" : 0,
"needTime" : 1,
"needFetch" : 0,
"isEOF" : 1,
"keyPattern" : "{ RoleLst._id: 1.0 }",
"isMultiKey" : 1,
"boundsVerbose" : "field #0['RoleLst._id']: [200, 200]",
"yieldMovedCursor" : 0,
"dupsTested" : 0,
"dupsDropped" : 0,
"seenInvalidated" : 0,
"matchTested" : 0,
"keysExamined" : 0,
"children" : []
}
]
}
]
}
}