Opendistro KNN score giving different scores on the same query vector

Question

I am using “cosinesimil” as the knn.space_type in opendistro elasticsearch version 7.8.0. I indexed 3 documents with attribute type knn_vector(the only other attribute supplied other than the knn_vector was a status term with value 1). The 3 vectors for these docs were (2,2), (2,1) and (2,3).

Surprisingly, when I search for the vector (1,1) [with a post filter of status = 1] using the query:

{
  "size": 1,
  "query": {
    "knn": {
      "embedding": {
        "vector": [1, 1],
        "k": 1
      }
    }
  },
  "post_filter": {
    "term": {"status": 1}
  }
}

I am getting different recall vectors each time I execute the query. Sometimes , I get the doc with vector (2,1) with _score 0.5, while other times I get the doc (2,2) with _score 1.0.

Questions:

1. Why am I getting different recall vectors when executing the same query?
2. Why is the _score for doc with vector (2,1) from elasticsearch coming to be 0.5. Only cosinesimil should be influencing the score and cosinesimil between (2,1) and (1,1) is around 0.95?
3. When using the same ES query with knn parameters k = 3 and size = 3, and execute it multiple times…sometimes I get the doc (2,1) with _score 0.5 and some other times I get it with score 0.95(the actual cosinesimil).