Count of items matched in array in elasticsearch aggregation

Elastic Stack Elasticsearch
5

Still am not getting actual count, this is my mapping

My mapping:

     {
"mappings": {
    "Process": {
        "properties": {
            "ProcessInstance": {
                "type": "nested",
                "properties": {
                        "_status": {"type": "string"},
                        "AssignedTo": {
                            "type": "nested",
                            "properties": {
                                "_id": {"type": "string"}
                            }
                        }
                }
            }


        }
    }
}

}

My Query:

{
"query": {
    "bool": {
        "must": [
            {
                "nested": {
                    "path": "ProcessInstance",
                    "query": {
                        "term": {
                            "ProcessInstance._status.keyword": "InProgress"
                        }
                    }
                }
            },
            {
                "nested": {
                    "path": "ProcessInstance",
                    "query": {
                        "term": {
                            "ProcessInstance.AssignedTo._id": "sangeeth"
                        }
                    }
                }
            }
        ]
    }
},
"aggs": {
    "ProcessInstance": {
        "nested": {
            "path": "ProcessInstance"
        },
        "aggs": {
            "_status": {
                "terms": {
                    "field": "ProcessInstance._status.keyword"
                }
            }
        }
    }
}

}

It returns nothing. Help me to get the matched count from array. I worried about this issue for past one week