Confidence Scores change once on updating the object, then change again on another search query with no conditions changed

Hello,

We are using Elasticsearch for our business solution. The problem we are facing is that, once an object of the index is updated, the search gives some score (Pic 2), and on searching again - keeping every single thing the same, scores change. From thereon, i.e after that one change, the scores remain static (We're using 2 shards).
This has been causing us major troubles. Any idea why does that happen?!
Pic 1 - Original Scores (The Upvote button updates the Index Object)

Pic 2 - Scores Generated

Pic 3 - On second search, the scores change - after this search the scores remain static.

What can be the solution to this problem?
If this is because round robin shard process, then why does it happen only once?
Even if I use preference with search, how to make sure that updates are done on the same shards from which are being accessed every time with the help of preference string?

Here's the mapping for your reference:
mapping = {
"mappings": {
"properties": {
"ArticleNumber": {
"type": "text"
},
"timestamp": {
"type": "date"
},
"introduction": {
"type": "text"
},
"file_name": {
"type": "text"
},
"RequirementsAndPreRequisites": {
"type": "text"
},
"SampleOutput": {
"type": "text"
},
"ScriptLogging": {
"type": "text"
},
"title": {
"type": "text"
},
"HowToRun": {
"type": "text"
},
"Title": {
"type": "text"
},
"UrlName": {
"type": "text"
},
"mop_url": {
"type": "text"
},
"Id": {
"type": "text"
},
"votes": {
"type": "text"
},
"feedback": {
"type": "nested",
"properties": {
"problem_description": {
"type": "text"
},
"upvote_users": { ---> This is Upvoted and changed
"type": "text",
"boost": 2
},
"downvote_users": {
"type": "text"
}
}
}
}
},
"settings" : {
"number_of_shards": 2,
"number_of_replicas": 2 }

}

Any help is greatly appreciated.
Thanks.