Integer Values Saved as Floats

[Zhenya]

I have Legacy application using Elasticsearch 5.6
Tried to duplicate it and I see that on my copy integer fields (including _id) are saved as floats
like

    curl --location --request GET 'http://localhost:9200/catalogsearch/_search'
   {
    "took": 10,
    "timed_out": false,
    "_shards": {
        "total": 5,
        "successful": 5,
        "skipped": 0,
        "failed": 0
    },
    "hits": {
        "total": 2,
        "max_score": 1.0,
        "hits": [
            {
                "_index": "catalogsearch_2020-04-29-22-18-19",
                "_type": "product",
                "_id": "13.0",
                ...

Items are added with integer values but saved like that 13.0 above.
Then when I want to delete by _id = 13 it can't find the item
I don't see any specific mapping instructions on any instance, but the difference exists
How can I make it save those values as integers?
Thanks