data can be found by some query on primary:

shard01:PRIMARY> db.XXXXXXXXXX.find({"task_ids" : [ NumberLong("6566381934111359492") ]})

{ "_id" : ObjectId("5b20be13e1803d1f2529dbe0"), "count" : 1, "task_ids" : [ NumberLong("6566381934111359492") ],....}

 

but cannot found by _id:

shard01:PRIMARY> db.XXXXXXXXXX.find({"_id":ObjectId("5b20be13e1803d1f2529dbe0")}).count()
0

the other secondaries are ok.